First off - Is your buddy alright? Any damage to his fleshy parts?
Lots of possibilities - It's hard to tell from what you have posted. Since he was shooting handloads the immediate thought runs to something that was caused by human error. Having said that though I have seen one occassion where a bought lot of factory ammo had a bad series of primers. The primers in question were "overpowered" for lack of a better term and the resulting ignition pressure caused a sporter model barreled .270 to split open like a banana. Everyone at first thought it was hand loads that did it, but since the guy still had the box of ammo and the receipt from Sportco, we did some investigating and found it ( F.f.F. ) FUBAR from Factory.
You said he "bought" handloads? Was it from a reliable company, or did he buy some off of a guy at the range or something?
With the casing ripping, it's possible it was the wrong powder. It's also possible that it had a double shot of powder. It's late, your reloading, you hit the powder, then forget, or get interrupted, and you hit it again, then seat the bullet without thinking. I personally had it happen a couple of times but luckily the grain count was high enough that the second shot wouldn't completely fit in the shell.
It's possible he had a thin walled case. Rare, but possible. Just too many variables I am afraid notdku from the information.
Got any pictures?