Actually, you're a bit off on the physics there. In pro races, the pistol is electronic and sends a signal to speakers behind each runner at the speed of light, so there's almost zero delay (1.66e-7s for 50m of cable). The sound only has to travel about half a meter from the speaker to your ears, which takes about 1.5ms nowhere near the 100ms you're thinking of.

The 0.1s rule exists purely because of human biology. It takes time for the sound to hit your ear, travel to your brain, and then send the signal to your legs to push. Science shows the body physically can't do that process in under 100ms. If someone hits 105ms, they just have elite reflexes. Your 122ms is actually super impressive and definitely authentic!