the lighter

Matthew is caught fidgeting with a Zippo lighter at the dinner table and proceeds to ramble inanely about how its dimensions somehow magically reflect the cosmos. The father tells his son and daughter, "You have an interesting friend here, more interesting than I suspect you know." Immediately I didn't think much of this scene. But then I realized that the father means "You have a stupid friend here, but I don't care, and temporarily he's useful to me." And he takes what's been said as a handy cue to have a go at his son. Before this the son and daughter had apparently quite enjoyed Matthew's spiel. Was this because they thought Matthew was deliberately taking the piss out of their father (and so wasn't so stupid) or because he was sounding stupid (because he was stupid)?

"I beseech ye in the bowels of Christ, think that ye may be mistaken."