The point with the wheel gun wasn't that it hadn't "fully" tightened (to
its limit), but that the particular gun wasn't generating enough torque
and, hence, wasn't tightening.  The suggestion was that there was a
problem of supply of compressed air to that gun.

So, suppose it works by detecting when, with the button depressed and a
fully open valve, the gun stops turning... The gun would have stopped,
but the nut would be loose.  The pit guy drops the gun to try to grab
the standby...and the lollypop says "go".

Given that guns fail on a semi-regular basis (hence the presence of a
standby gun), that would seem boneheaded as a system.  Far simpler to
assume the person in charge of the release saw the gun go down and
misinterpreted the gesture - which was a bit wild - as the wheel being
on.  Screw-ups are very easy when under that kind of pressure and with
the speed involved.