That would be on me. The whole line, in Project II, is "That's the name of your mech-flies?"
I thought it would be strange for Giott to know what ships are in the first place, 'cause aside from the airship dock in the Dwarf Kingdom (Why is that there, by the way?), there's no evidence that the Underworld has any idea of what ships are, much less airships. I assumed he'd know what machines are (Tower of Babil) and he'd know what flies are (Flying enemies in the Underworld), so he'd call them "mechanical flies". There wasn't enough room for "mechanical", so I shortened it to "mech". No errors at all.