[Miles]

Not an 18 series either, but all I do for Uncle is work on his guns .

With only the one picture to work with, we can see that the slide and barrel are still in the locked, forward position and the barrel is still visibly intact.
We can't see if the chamber area is cracked, or if the barrel is bulged from stuck bullet.

So, at first impression, it looks like the case head blew out and everything went down the grip.

Seen that before!

Single cartridge defect?
Previous cartridge undercharged, put the bullet up the barrel and the next one blew?
Barrel ramp/chamber out of spec?
Without looking at the gun, one can only speculate.
But I sure would sequester any more rounds of that ammo, if any's left.

Like others have written, contact Glock and see what they want to do.
Since it's a Gen4, your shooting buddy might get warranty service or a reduced price on a replacement.
I'd also contact CCI as well.