Meteorolical Winter vs Calendar Winter in that case. Though I'll agree "true" isn't the right term, it's clear that Square Enix is using Calendar Seasons. Which are dictated by the Solstices and Equinoxes, rather than what the weather happens to be doing.

For example, outside yesterday where I live it was 77 degrees farenheight. That's a temperature most associate with late spring or early summer. Doesn't make December 2nd suddenly Spring / Summer just because the meteorlogy is being screwy (and the week before it was 40 degrees)