Ghosts!!
j/k.
Diesel engines don't need spark plugs or anything like that, so I guess a similar thing could happen on a nitro car.
Oh yeah, I've had that happen too, but I thought that I did have a glow ignitor on so I didn't think about it at the time. Until the next time I fired my engine up, I realized my glow ignitor was still at the bottom of my pit box.