I’d like to read more about that hypothesis.
The Ordovician extinction was due to massive and worldwide glaciation that came on kinda sudden-like. I don’t find gradualist models for ice ages compelling.
There’s an iridium abundance in the terminal Ordovician stratum, but this is regarded as inconclusive (it sez here). Iridium abundance (as well as chromium) is attested at the K-T boundary, pretty much everywhere it’s been studied since Walter and Luis Alvarez articulated their theory. Iridium is also associated with the Eltanin impact which happened circa 2 million years ago.
A supernova more or less in proximity would generate (among other things) Plutonium 244 (it sez here), which is sufficiently long-lived (half-life is 80 million years) to be possibly diagnostic of a supernova explosion.
The documentary (actually a series) that I had watched was Mega Disasters (after a quick search - episode 15 from season 2) titled Gamma Ray Burst. That series was a little over the top (65% hyperbole/ 35% hard science), but entertaining nonetheless.