Panel 1: We find ourselves at the hotel watching John get all gobsmacked because the lobby is packed. Since he's never seen the hotel so busy before, he assumes that the Shriners are having a convention too.
Panel 2: When he goes to check in, the lady at the counter tells him that sorry, there is no reservation for a John Patterson from Milborough, Ontario on file. Since John is certain he booked, he tells her that there must have been some mistake.
Panel 3: We get a foreshadowing of the "Yes....but not by US" thing when she tells him that they're booked solid and every other hotel is full but does suggest asking to double up with a member of his group.
Panel 4: We find him in Doctor Shotgun's room staring at a single bed and being told "Maybe there'll be a cancellation before we turn in."
Summary: One of two things happened. Either John thought that he made the reservation but didn't OR there's a reservation for a John PATERSON from MILBORO, Ontario on file. There must be some reason that isn't Lynn being pissed at being called Johnson all the time that explains Mike's need to say Patterson with two t's.
ETA: It occurs to me that we're starting to see John being made into what turns out to be a (non-existent) threat today because Lynn keeps hammering home what a bad mood he's in because the convention was a bust.