You're both correct. Public perception of seasons is about a month off from the actual season to season transition.
@CaptainAmerica is correct that Disney HAS to use the official seasonal dates, but
@JusticeDisney has a good argument inasmuch as the seasonal opening time frame may not be the best way to communicate information to the general public. I don't like "3rd quarter" of xxxx since that sounds too much like I'm at work. Maybe they could just use "early", "mid", and "late". They clearly want a lack of specificity with the dates (I would too with overseeing such large complicated projects) and dividing the year into thirds instead of quarters gives them even less temporal resolution. Anyway, sorry to interrupt the argument.