Michael does know what they mean, actually. And it makes his stomach flip. He feels, strongly and suddenly, that this conversation can't be allowed to end here.
“You're not bothering me!” he exclaims, abruptly shoving his book and a notepad and pen off his lap and onto the ground. “I'm not doing anything! You can, uh, sit down, if you want. To, you know, rest, or for any other reason. Trust me, it's a good bench, I come here a lot.”