Well, the last two posts are just wrong.The chamber opening is on the right side of the rifle. The piece of lead hit him on the left side of his face after the round was fired.
I've seen it happen quite a few times with .22 LR and a few with jacketed bullets - far more times than a 50 yard return of a particle with substantial aerodynamic drag.
And when I've experienced it or seen it happen to other people, it has always been a curved and oddly-shaped piece of lead (or jacket).
I have a video that I shot last year, in which I caught close-up slow-motion of an Out Of Battery (OOB) discharge in an AR-22.
When the OOB ruptured the case, a twisted and slightly curved piece of it (about 1/16", tapering up to 1/8", by about 3/16" long) flew out of the gap between the bolt and chamber, up, back, and around the upper receiver, and hit me just below the left lens of my glasses. It drew a little blood and got caught in my mustache.
Two years ago, a friend of mine was standing about 7 feet to the right and behind another friend that was shooting a Calico M900 (9mm carbine version). Top-feed, bottom-eject. Something "popped" in the Calico and the friend standing behind grabbed his face.
Long story short, the case ruptured and a rather small fragment of the case web managed to twist and fly its way not just up, back, and over to him, but around his safety glasses and into his right eye.
He is now blind in his right eye, even after multiple surgeries to try to save the nerve.
JohnKSa does make a good point. The fragment that your friend caught could have been a larger object that only left behind the sliver. I have caught many bits of ricochet debris in my life, and many of them left no debris or only small fragments where they contacted me.
Found an interesting caveat on a steel target seller's website. They stated that none of their targets are rated for "subsonic rimfire ammo". I'd never thought about that, but I guess they're saying that if the bullet isn't moving fast enough, it may not fragment sufficiently on impact with the target to be safe .
I bought a rather expensive "rimfire" target set that was highly recommended.
Rated for "all rimfire rounds - rifle and handgun".
No, I did not go stupid and start smacking them with .41 Swiss RF or .44 Henry. That is not where this story goes.
During a practice session with my son and our .22 LR match rifles, I pulled out my Marlin 882SS in .22 WMR and fired a magazine or two.
As we were packing up later, I noticed that my KYL targets were bent, and a few of the hanging targets were cratered and bent.
I sent an email to the manufacturer, asking if they were actually rated for "ALL rimfire" cartridges, including .22 WMR, and possibly .17 HMR and .17 WSM, not just .22 LR.
His response was, roughly, "Those are hunting cartridges. Nobody shoots targets with those! My targets are for .22 rimfire only!"
After a few more emails back and forth, he still could not understand that ".22 rimfire" and "all rimfire" is not the same as ".22 LR target ammunition only".