I guess I should clear this up as I see that Portfolio Day isn't a widely know thing.
Portfolio Day is a series of events spread over the country where art college representatives gather. Potential college bound hopefuls go to these events to get their portfolios critiqued. You can also compare and contrast various colleges and get a general idea of which ones you want to apply for.
Portfolio Day is a great event for finding out what areas you need to artistically improve on, and what colleges offer the programs you're interested in.
BTW: I think this tactic seen in this comic is called a "bait and switch"