Cal is back to not understanding at all how Tony doesn't see what an asshole Obadiah is. It's not like spotting assholes is some kind of special Chandler superpower. You just need to have eyes.

The mention of books gives him an idea, though. He glances at Sherlock as says quietly - as if he thinks that dropping his voice will somehow make it impossible for Tony and Obadiah to hear him (he doesn't) - "I do have that test I wanted to study for. We wouldn't have to stay long."

In other words, it's a perfectly legitimate excuse to eat quickly and get out of there, which allows everyone to - almost get what they want. The fine art of diplomacy in action!