It could have very well been in December. The problem is that the Roman and Jewish calendars don’t match up quite right, and they both drift in relation to “our” calendar (leap days and such).
Stuff like this makes dating anything more than a few hundred years ago problematic. Seriously.
No... Sukkot is the full moon of the seventh month, as determined by the ripening of the winter barley in the spring. "Leap" could push it forward 29 days, the sighted moon could push it forward one more day (two, some may argue), But not all the way in December, not to mention the end of December... What MAY be considered to correspond to christmas from time to time is Hanukkah (25th of the ninth month).