I think that should have read: Long before the Christians
Yes, xmas was moved to coincide with Midwinter festivals, which just about every culture has celebrated.
Anyway, I'm an atheist too but I don't get all twisted about "Christmas". Sure it's based on a religious festival, but the holiday has a huge secular component nowadays. I even sing carols like "Silent Night" because I like them. And because my singing can drive a bagpiper to suicide