I think maybe I MIGHT have some understanding of the perspective of this chap... not saying this is the case, we don't know his exact reasons for not celebrating, and it may well be he's just being rude, but I'm just looking from a different angle.
For various personal reasons (too long to go into here) I decided I really didn't want to celebrate/get involved in Christmas this year as I'm finding it far too painful and upsetting. I don't begrudge anyone else celebrating it but I really just wanted to carry on and let it get past as quickly as possible as a normal day - I still do.
I told people a while back that I wished them a happy festive season, and a lovely time celebrating it, but that I really didn't want to "do" Christmas this year as it was too upsetting (they know why) and please no cards or gifts as I didn't want to get involved in all that, so I politely suggested they save their money for their own treats/celebrations/gifts for their families etc... as I don't want anyone wasting their hard earned money on me at an already very expensive time. I've made it clear in a friendly way - not in a miserable rude way - but politely and respectfully, that I really am not doing Xmas this year and I don't want to participate in parties, meals, gifts, cards etc... any of it. I'm happy just having a quiet time and catching up with stuff.
Notwithstanding this, I've had cards, gifts etc... from people who know all of the above - which is very kind of them and I've said thank you and accepted them graciously - but it's made me feel a bit embarrassed and awkward as I've not got cards or gifts for anyone. Me being me I've then had to rush out and get cards and gifts for people to reciprocate - and suddenly I'm participating in Xmas whether I wanted to or not. I know there's no obligation to do so, but I always feel if someone gets me a card/gift at xmas it's polite and appropriate to return the gesture.
So I guess what I'm saying is that this guy and his family have for whatever reason(s) decided not to celebrate/participate in Xmas - but if they then start getting cards etc... they may feel they should be reciprocating and they are then drawn into participating in xmas even though they don't want to - or they feel embarrassed that they won't be reciprocating.
Not sure I'm making sense, and I must make it perfectly clear that I know no one HAS to buy cards and gifts for others, and yes, it is the polite thing to do to graciously accept such things if given - it's a lovely kind gesture - I recognise that. But this year I've seen a bit of it from the other perspective so I kind of understand I suppose. As someone really struggling with Christmas this year I guess I've noticed more than ever how much there is a general assumption that everyone is happy and excited for Christmas and there is a tendency to forget that some people don't celebrate it or indeed, for some people, it's the worst, most painful time ever and they just want it over with and to pretend it's not happening.
Not saying the OP is right or the chap in question is right... I have no idea about what goes on in his life - we don't know if it's a religious decision (he's atheist - but so am I and my decision this year has nothing to do with that - I usually do celebrate) - or whether there is a life event that has made Christmas a particularly difficult/upsetting time - I'm just offering different viewpoints on something that may not be quite so black and white.