Recently a large male deer who appeared to be perfectly healthy approached me while out for a walk. Would it be safe to assume this means someone has been feeding it regularly or is this behavior not all that uncommon?
It's certainly reasonable that the deer could be acclimated to human contact, possibly having been fed in the past.
It could also have been a territorial response- this has been documented more than once (https://www.jstor.org/stable/24875694 for an example). If you're in the northern hemisphere, October through January is rutting (mating) season in many areas and male deer are often more aggressive than other times of year.
Deer are often quite curious and inquisitive, though it seems to vary by species. Possibly it was just interested in checking out the strange object in its environment (you).
I've had mule deer (Odocoileus hemionus) walk up right behind me while I was not moving- quite a surprise! Crowds of mule deer have often hung around while I was cleaning a shot deer, as well. Whitetail deer (Odocoileus virginianus) have seemed more skittish in my experience (source: a couple decades of hunting and living around both species).