My point is not that heavy volume is required for this to happen, and it's strange how you could jump to that conclusion.

Instead, a higher rate of fire gives more opportunities to witness anomolies between shots, within a given time. Combine this with tracers, and now you can easily follow these paths, before and after each bullet hits it's initial target.

With a 6000 round-per-minute minigun, even if you only see one tracer bounce away every second, that demonstrates a 1% chance for every round to deflect and hit somewhere unintended.

Considering that the tracers are normally spaced out on a belt, with other rounds between them; the sample size can be reduced further, and this chance becomes multiple times higher.

When yearly machine-gun shoots were still hosted in Knob Creek, Kentucky, the range staffed people left and right of the firing line with fire extinguishers. After the 'finale' occurred and weapons were cleared, they would run out onto the hills beside the range.

With multiple miniguns firing alongside other automatics, and the insane number of rounds fired downrange, it was inevitable to have more than enough hot tracers land in the brush of these hills to start multiple small fires.

The possibility of ricochet injury is simply matter of probability. Sure, I would never claim this is the most probable explanation, but it's silly to claim there's absolutely no chance this could happen.