I've read a number of opinions since posting this and I have to say that I think the top answer is conservative to the point of absurdity.
According to a strict reading of the FDA food safety rules, yes this stock should be considered a lethal poison. However there are a number of mitigating factors here, which I believe render this food completely safe. The FDA rules will keep you safe, but they are written to keep you safe under any circumstances.
To be clear, after cooking there were zero bacteria in this stock or on the stockpot. There were zero botulism spores in the stock or stockpot. Pressure cooking on high for an hour has completely eradicated everything. So the only potential source of contamination would have been from airborne bacteria or bacterial spores happening to float through the extremely small aperture of the vent after de-pressurization.
There is probably a tiny bit of ongoing air exchange due to convection between the heated air inside and cool air outside the pot. All told though, this is clearly going to be a tiny amount of air overall. Heck, let's say it's a few liters, which I think is generous.
So, what we're terrified of here is that there was enough airborne E. coli or botulism or something evil in a few liters of kitchen air to colonize a stock to the point of being unsafe (even with reheating) in maybe 5-8 hours. I have to believe that if that was even remotely possible, we'd all be dying left and right simply from breathing our kitchen air for more than a few minutes at a time.
Do what you feel is right, but in my opinion saying to throw this out is 100% about fear of legal liability and 0% about science or sense. Yes, I ate the stock. It was delicious. YMMV.