Suspect on what basis?
You clearly have no evidence of this otherwise you wouldn't have to suspect anything, you'd simply lay it before us. So suspect on what basis?
Because they either admit to following religious aspects, or do not deny it - in case you haven't noticed. But then, you are probably too busy visiting various religious forums.
No, I haven't noticed atheists following religious aspects of Christmas. Which atheists and which religious aspects are they following? Specifically, I mean.
Never sent or received a Christmas card, or been to a carol service, or nativity, joined in with carols, or just enjoyed listening to them, given or received Christmas presents, said "Happy Christmas" to someone, etc, etc. Any atheist who denies doing any, or all those things, is an arrant liar.