Welcome notnothin!!!
About your question. Yes, May is typically near the end of the school year, so therefore, it actually is one of the better times to go to Disney World. Most of the people going to Disney during this month are people who are in college (who get out in early May) and are people who don't have children. (Note I said most, not all). There are also a few select schools who get out early in May, but there aren't many. So, truthfully, your assumptions are right.
The reason it seems like May is going to be so crowed (and most likely will be more croweded than past years) is because of the Happiest Celebration on Earth celebration. Since the celebration begins on the 5th a lot of people are going to want to go during the month of May to see it before the summer crowds get there.
I hope I helped explain this a little better.