Immediately, Jack Frost and Pyro Jack come to mind, and Heat frowns. Jack didn't look like either one, but that didn't mean there weren't more than one each. "That's your name, not the name of your demon?"

Or it's a coincidence. 'jack' had to come from somewhere.

"I'm Heat. Actual name." Since he just asked if Jack was his name or his demon's, reasonable to clarify the same for himself.