Prior art isn't a defence.
The story kinda misses the point. Prior art is all very nice, but it can only shoot down IP claims one at a time. You claim "X", I show prior art, "X" goes away, you claim "Y"... You get the idea, until I can't find any prior art - then I'm in trouble.
I get my own IP.
You claim "X", I say "fine - what about Z?". You say: "oh drat, why don't we cross license our IP?" I say "Fine, we'll do that".
Just showing prior art, is fine - but if I can shoot your product out of the water too with my IP, then we'd better make a deal.
Of course, this doesn't help you with IP trolls, who never make any product - but that's a different story.
Now could Red Hat become a turncoat and use their IP against other companies? Yeah, they could. Is that likely? No, not right now (they're selling product). Of course, things change. However, what else is Red Hat to do? The real test is will they use their IP to help another Open Source Company? That's trickier to answer, and that's the acid test.