Turns out just shitty craftsmanship. Wires were fine, loose wire nuts caused it to short over time. Atlease it was an easy fix only $35ish for the new fixture
Discussion
Had an identical experience with mom's shower fixture. She swears hand to God that it was the original bulb from when the house was built 40+ years ago. Installed new bulb and it popped instantly. Opened it up and saw the same thing.
Half of the receptacles in the house had signs of arc flash burn from the old stick-in mechanism failing and releasing the wire.
I had knob N tube, cloth 2 wire, and some Romex was put in for some celing fixtures previous owner did. Took some time to replace it all.
Looks like they turned the neutral into the hot 🥵