Yes, Graduating in May counts as being full time from Jan-May. You were still an enrolled student. So you meet the 5 month rule.
Full time student has two meanings* in taxes. First, the five month rule must be met (if you are over 18) for you to be a "Qualifying Child" dependent on your parent's (or other close relative's) tax return. Hence the question in the personal info section. To claim a tuition credit, you only need to be half time or more, and for no specific time length (basically "full time" is meaningless in the educational expenses section).
*There are third and fourth and fifth meanings having to do with the "kiddie tax", eligibility for the refundable portion of the AOTC and eligibility for the Retirement Savers Credit.
