It's not "mistaken to mean something in a different language". The name literally originated as religious reference.
You're just mistaking the word's origin for its meaning. That's just not how any of this works.
In both languages (English and German) the name has the same origin I believe, and the same current meaning of a name that doesn't imply the person is of the Christian religion. I think it's wrong to say that there's a language confusion of being too religious, since the name has the same religiosity in both languages.
Seems to me the same as was done by Christian: mistaking the Santa hat of 2019 with whatever happened before.
It doesn't constitute trolling by itself, but it does imply he's not Muslim or Jewish, which narrows down possible reasons why he might be offended by santa hats.
Not to suggest that most Muslims or Jews are offended by Santa hats.
As for the rest, the net result is very much trolling even if it wasn't the original intent.