I think he's thinking of "freewheel" but "flywheel" came out. Simple mistake. Don't give him too much of a hard time.

At least he's in the ballpark. Most people call a derailleur a chain-gear-shifter-thingy. I know a girl that called tires "wheels" for a year. "I think I need new wheels, mine are really worn down after 6 months." Some people call cogs "rear chainrings", etc...