That is truly frightening! That is kind of why I never went to an indoor range ever again, I kept noticing all the bullet holes in the dividers. Nuh uh, nope!
The last 3 gun competition I was in locally invited a lot of new shooters to enter. Kind of went the same way, people (including myself) were getting pepper sprayed by shot bouncing back off the targets every so often. No one could figure out what was going on for a little while until we realized that a couple of people were using steel shot instead of lead shot.
I even managed to get sprayed with shot while shooting sporting clay. I'm not sure how it happened but one of the stations across the quarry must have hit me as I was leaving my station. Luckily I had a backpack on carrying station to station, because it still stung like hell. Shotguns must hate my own guts or something.