Well I can't find a Captain Lowe in Mac and Shads.
As Haynes is refering to selling the horse the PI rode on the day that would be Tommy the grey.
Trying to give Haynes the benefit of the doubt he could
have sold him a n other horse and he could
have been attched to the colonials hence being mounted and being under a Captain Lowe (if there is one in the Colonial listings) though why would he say he was RA?
Looking at the other campaigns he claims to have been in ie Majuba I have checked the other Regiments who were there such as the 2/21st, 58th, 94th and all I can find is a Private 1002 W Haynes no clasp in the 2/21st
I think this story is not right