I've never been in the military, (apart from the army cadets in my youth), but I wouldn't know what a rocket propelled grenade looks like. I once ripped open the end of my finger though on some kind of detenator. I found it in the street, it looked like a torch, without the lens/bulb etc. A long black handle, a wider flat end and on the handle, a spring loaded switch type thing. I just walked up the street flicking the spring loaded bit back and forth, until I eventually pulled the switch to its full length and let go. The wider end blew with a deafening bang. Luckily I had the thing pointing down and away from me at the time, but I did have the index finger of my right hand on it which was slashed wide open. I dropped the thing very quickly and ran away. I was in Salford at the time and had to get a bus back to Bolton, (late night and the trains were off therefore a rail replacement bus was provided). By the time I got back to Bolton an hour later, my finger was still bleeding, so I went to A&E to have it stitched.
I rambled a bit haven't I? anyway my point is that although it sounds like a stupid thing to do, he might not have known what it was and therefore had no reason to suspect the thing was gonna blow up in his face!