Wow! I did not even realized it was not even present!

Always wondered why he was hollow but McDuff wasn't, even though McDuff's dialogue is decidedly more hollow-esque. Did they mix up the blacksmiths by mistake?

its because mcduff had lost purpose, but lenigrast hadn't you meet only a bit after he was locked out

technically, most NPC are undead

lenigrast is a bit advanced on the physical side, but grounded by his work and his daughter, other like maughlin and cale are grounded by their passion and issues (but go hollow mentally once those are resolved), lucratiel is starting to be cursed physically and lose her memory slowly. some are unaffected and maybe human, some are part monster (emerald herald : dragon, nashandra: dark, navlan, aida)
the only "confirmed" non undead human is felkin ("this is a land for undead... and a few madmen like me").

His main purpose is to smith weapons. It's what he enjoys and does all the time. Why would he go hollow then?

This is true of all the smiths. They have a singular purpose that always needs fulfilling,
and they do fulfill it, so the curse doesn't quite affect them the same.

Bugger off. Vamos for life.

Andre is bland and uninteresting and is only loved for the same reason Solaire is. Nostalgia and rose tinted glasses.

Andre and solaire are both friendly and likeable, Leningrast is the dude who keeps trying to tell you about “back in my day”