Obama's full comment absolutely makes no sense if not in code.

It does in a campaign sense, many people working on political campaigns have to put in the legwork and make phone calls to talk to potential voters, donors, so on. In a basement might be hyperbole, or maybe they are literally in a basement. Eating cold pizza would be literal because conditions are tight and you're eating leftovers.

So overall context would be on one hand you have a celebrity singer performing at an event, that makes one imagine a spectacular, high end type fundraiser. Then on another hand you're in these less than ideal college student conditions trying to get people on the phone to donate. I think he's telling Democrats to get their head out of their ass and get back to the grind, "grassroots" and all that. He recently had a quote telling dems to "stop whining". So it fits the tough love theme.