Glad you're OK!

There's a hard expansion ring around the case just ahead of the blowout. It looks like the gun fired just slightly out of battery.
If that case was previously fired out of a gun with a looser chamber than yours, and was then resized in a carbide sizing die, it may have remained a bit oversized near the web.
So, it would've jammed just short of being fully chambered.
The disconnector should have prevented the gun from firing.

An alternate explanation is that it was an overload and the case head blew out. But, if that happened, typically the magazine is blown out, the grips are splintered, and you might have a hand injury.

I "second" your idea to cull and discard other people's fired brass from your own Starline brass.

You should have the disconnector evaluated. If it was defective or worn, that could be part of the problem. But, a full evaluation of the whole pistol is likely a good idea.

Best Regards,
Jim