Wow, I've never heard of that! Perhaps it's just an odd coincidence. Where do you live? The Italian Beef sandwich was actually created in Chicago, by Italian-Americans, not in Italy
Being a native Chicagoan, I have never heard of eating Italian Beef at Christmas!
We had vegetarian lasagna at my aunt's house tonight, which was a little odd for a Christmas meal, but...my parents griped about it the whole way home! I didn't mind it...It was still yummy, even sans meat.
Tomorrow, it's traditional Christmas ham with the other side of the family