Even if Erickson is absolutely correct, I do think the co-opting the Winter Solstice resonated with the early Christians & contributed to the choice & why Jesus' birth (rather than,say, baptism) was fronted.
Lots of religions mark solstice & equinox.
Today we see the same thing happening with Halloween.
I think there are pagan roots to Hallow e'en. For a few centuries the Church tried to gain control of it, making it the eve of an "All Saints Day".
Now with serious reemergence of paganism, Christians are having their own "Harvest Day Festivals" in their churches, where kids dress in - guess what? - costumes (but no evil themes). Nevermind that there is already a Christian-rooted Harvest Festival a few week later (or earlier in Canada. Harvest is in October in Edmonton.)