I'd take their word on it if it weren't that they got so much wrong.
If there's a weight gain, why is there a weight gain?
In party, loneliness might be an answer. You're finally free from home, free from your parents, able to do whatever you want, a grown up who doesn't need anybody and -- You're parents aren't around. Or you're brother. Or you sister. Or . . .
So you might eat out of depression (or out of being nervous).
Equally true, at home you may be required to eat certain things, certain kinds of food. X number of leafy greens, X number of carrots, etc.
Now you don't have to. The closest this freedom was captured was in two brief sections about pizza late at night and 7-11 late at night. But when you're in charge, you can eat at any time, eat anything you want. It's heady and just like you can overdue other things, you can overdo what you end up eating.
As in: I'm hungry. Forget the turnip greens, I'm in a hurry, I'll just have that burger and some fries. And at home you might have eaten that but not every night. But Mom and Dad aren't there now to check and make sure you eat the needed stuff along with the fun stuff.
Now it's all on you. And that's how you can end up gaing weight.
"Iraq snapshot" (The Common Ills):