I'm not sure on this. There are plenty of people who don't 'do' Christmas. There could be all kinds of reasons. Resisting being coerced into consumerism for the sake of salesmen is one, and a persuasive one given the Climate Emergency.
Of course mum squeals with excitement over the idea of doing things her way, and of course you believe everything should be her way because you have no unpleasant feelings about it. Your partner wasn't brought up by your mum. He feels very different.
You pretended to agree with him and not attempt to 'do' Christmas the way salesmen and your mum do it, but all the time you were determined to go your/your mum's way, but secretly. I'm not sure why people think others who do things differently are in the wrong and bad characters. If the man had a different religion he wouldn't do Christmas. If he had a different background and hateful associations with that time of year, he wouldn't do Christmas.
Others ask if the drinking is a habit, or only at Christmas. Of course you need to wonder about getting involved with an alcoholic. But, if you had said he is teetotal, then the same people would have made exactly the same type of accusations about him being joyless and not knowing how to have a good time, and being no fun.
Has he been unpleasant to you or in the wrong in any other way? Is it merely because he doesn't join you in being childlike about what Santa will bring? (And he doesn't buy the curious idea that everyone in the country must be forced to eat turkey on a certain day of the year by order of salesmen)
Would he buy you something if it happened that you saw it in a shop window simply by chance, fell in love with it and really wanted it, but hadn't got money with you? That would be genuinely for the pleasure of pleasing you. Xmas trinkets are like forecourt afterthought red roses, just to conform which instructions from advertisers.
You have an agreement (he thought) that neither of you would buy 'stuff'/ non-essential and unwanted things, merely because an industry of marketing has grown up to fill landfill with Christmas junk. As someone said, he can't be a mind-reader. A lot of couples and families whose houses are already stuffed with all they need or want will agree to donate to whatever charity their partners or siblings nominate, instead of buying 'gifts'.
An ex partner detested anything to do with Christmas, and plenty of others do too. We sometimes fled the country trying to avoid it, and found everywhere full of fellow Christmas-haters, often thwarted by relentless hotel staff attempting to 'please' the Westerner guests by providing a version of Santa and a tree and a turkey and enforced jollity and song.