The light beam that starts the clocks (the one that will give you a red light, if you roll out of it too soon) would only see a belly-pan as an extension of the wheel, and couldn't red-light you because that light beam would never make it to the photocell... blocked, first by the wheel, then by the belly-pan. You can only get a red light from that light/photocell combination when the photocell "sees" the light beam before the green light comes on.
HOWEVER, the clock makers were aware that this could be a problem, so they incorporated a second light/photocell called a "GUARD BEAM," that is placed a few inches (I don't remember how far, exactly, but, it's not much...) farther down the track from the e.t. light/photocell... and IF your wheel hasn't rolled out of the e.t. light's beam when your front tire breaks the guard beam, it gives you a red light, because something is blocking the light to the e.t. photocell... and, it should not be....when your car has travelled that far.
That is probably what was happening to your friend, with the belly-pan/red lights.
My car is just a junk, Bracket car and I don't run it at NHRA tracks; they'd just laugh at it....
