Christmas and New Year's are treated in reverse to Western customs. In America, Christmas is for family and New Year's is for partying. In Japan, Christmas is for partying (and dating) and New Year's is for family. Note that Christmas is not a holiday in Japan.

Is it rude? Not necessarily. Not all Japanese families get together on New Year's; some aren't able to afford or willing to travel home and some decide it isn't worth it when the parents have already decided to fly to Guam for the holidays. If your friend really has no plans for New Year's, he'll probably welcome a chance to at least spend it with a friend he hasn't seen in a while.