Range brass is my first thought. Coupla years ago a notorious scrounger at my IWLA range totaled his upper with a reloaded pickup case. He even fessed up about the likely cause.
Schitt happens, but happens less to the prudent. Let us know what he says.
Range brass is perfectly fine, if you know what you are picking up. Some is garbage and just stays in the dirt. The last time I picked up any, it was primo new once fired chidt. FC and PMC. That was a few years ago and that's mostly all I've been using since then. I think I picked up 1200 pcs of FC and 600 pcs of PMC. I made it a point to shoot the FC range pick up brass in the black rifle challenge here. If you don't know what you are picking up, leave it lay. Sometimes there's a reason it's laying there. Secondly, I'm wondering if the rifle fired out of battery? Glad to hear no one was hurt as well.
