There are no records I can find as to exactly where Lt Browne was on his reconnaissance on the morning of 21st January. There is a thread on the forum on Lt Browne. The consensus seems to be that Browne was in the area of current day Silutshana settlement or possibly Esigqokweni. I only know that he managed to see a party of Zulus "Scouts and a small party of the enemy" (The Narrative) and as I recall from another source was fired at on his return to camp, which he reached about midday. At 5mph he could have travelled about 30 miles, Esigqokwene is approx 10 miles from camp ATCF a circuitous route and difficulty of the ground would increase distance and decrease speed, so "ball park" this fits.
The interpretation of what was seen has always been attributed by commentators to the main body of Zulus coming from Ulundi. It may well be so, but it may also be worth reviewing that in the context of the reconnaissance that was undertaken before and since arriving at the camp site at Isandlwana.
On 15th January a recon party went as far as iSipesi Hill, this on the line of the route towards Ulundi and the planned line of march.
On 17th Chelmsford himself recon to Isandlwana Hill and selected this as the next "halting place".
In the afternoon of the 20th Jan Chelmsford took out a recon party down to the head of the Mangene Falls the chasm of which the Narrative identifies (if my reading of it is correct) as "Matyana's stronghold". At this same time Chelmsford would also have seen the terrain and identified the very strong position later identified as the site of the new camp, to which preparations were ordered to move to on the 22nd Jan. Though no Zulus were to be seen in the chasm, what Chelmsford did see was enough to make him order on his return to camp preparation for a strong recon force under the overall command of Dartnell.
At 4-30am on 21st Jan the infantry element left to clear the Valley of the Mangene. An hour later the mounted troop left one part (Carbineers) went over the Hlazikazi Hill north of the Mangene, the second part (NMP) Mansel and Dartnell carried to cross the Mangene river and to look further up the Mangene Valley.
At 5-30am (presumably) the small (4 Men) mounted recon left for the plain in front of iSipezi, it was known by 21st Jan that a large impi on its way from Ulundi toward the 3rd Column. Lt Browne was IMI a regular and was likely a more trusted source on information than a Colonial or informer.
At around 4-00pm Chelmsford himself conducted a recon up to the plateau and at a point identified as Point B on the Narrative map (iThusi) saw for himself mounted Zulus in the distance at some 4 miles, in a location identified as Mabaso by writers. The Narrative states of Point B, that it is "one of the most advanced Vedettes" this infers there was at least one other as far or farther advanced, i.e. more distant from camp. It may also infer that this position was too far advanced (or not interesting enough) to visit. Chelmsford had left camp around 4-00pm (meeting Buller and Gossett on his way) so allowing for time to return to camp and failing light the Vedettes would be drawn is by around 6-45pm.
It is argued that there were no Videttes east of iThusi, the Narrative certainly in my reading allows this possibility, if not confirming it.
By 1-30am reports from Dartnell encouraged Chelmsford to detach the greater part of his force and go to his "aid". The account given by Chelmsford and his staff is that there were much larger numbers of Zulus down at Mangene that had previously been reported. In the three hours between receiving a note to this effect (if indeed it was to this effect) nobody other than those present when it was read to Chelmsford can have seen it, no copy exists.
It is believed that Lt Browne's report was ignored, it is almost an aside in the Narrative. It is just possible that is was not ignored, at least in Chelmsford's mind. If Chelmsford reading his reports and thinking of his recon knowledge of the last two days, summarised in the sum total of 14 mounted Zulus 4 miles distant, he may have reached the conclusion that the Zulus that Lt Browne saw were outliers or part of an impi going towards Mangene - Qedeni direction. The impi coming from the East could go either North or South from the iSipezi plain. Browne specifically reported Scouts, scouts infer a larger force nearby. The area behind Silutshana/Magogo was unknown to him and as we now know did contain large numbers of Zulus according to Col. Russell on the night of 21/22nd Jan, they though were probably travelling north not south.
By "bigging up" the 1-30am report from Dartnell Chelmsford uses it later to disguise the actual and in one reading of the informaiton available to him, logical conclusion he may already have reached, he was a man under much pressure, was showing signs of indecision and may have jumped to a conclusion. His decision is a hard one to explain.
Did Chelmsford just misintepret his intelligence?