I don't believe the video quite says this (I watched the relevant section).

It's worth noting that they are mostly interested in critical phenomena in general, and earthquakes are kind of a drive-by application, treated along with fires and sand piles.

They do hint around the edges, but they don't head-on make the claim for earthquakes that small EQs materially lessen stress buildup and thereby make larger EQ's less likely.

I was looking for a credential of one of the people they interview, to see if they are really a solid earth person or more of a critical phenomena person -- their names aren't easy to find. This particular myth ("small earthquakes relieve stress") is a bit of a stinker in the solid earth community, and I think a solid earth person would be quite careful about their words as they discuss this.

I think you've summed it up correctly. It's not proof and some scientists claiming some things isn't the same as studies/evidence. However, is there evidence that it's not true? The fact is we do have these smaller movements and earthquakes quite regularly, so we don't really know what would happen after a long absence of them (do we? I suppose there are simulations perhaps that could be run? But I don't know that that's proof either way). To me though it makes a lot of sense that it would/could spur a huge event.