Gabriel completely refraining from commenting is also a tip-off, yeah, though Seth isn't intending to push the subject. He doesn't need to know, doesn't really want to know the details. In his line of work, he's learnt not to ask too many questions he doesn't want to know the answers to.

He ends up just ordering the same thing as Gabe, for simplicity. "Ask me what?" he inquires after the waitress disappears.