Nothing made up, not sure why you'd say that... So here's an example to hopefully clear it up: my bucket is 14in diamter, that's 154 sq in. Applying 50lbs across that surface is 50lbs/154sq.in. = 0.3 psi. So your lid will hold whatever it's seal can hold plus 0.3psi. Looking at a few threads it seems that the lid blows at only a few , so let's say 3psi, so it will blow at 3.3 psi (just think how strong that is, 3 pounds on every square inch, that is over 450 pounds on the lid alone, so this is probably an over estimate). Looking at the solubility of CO2 at 3.3psi and room temperature gives 0.9 vol of CO2, which is only half the minimum recommended carbonation for a pale/IPA. Therefore it probably won't be worth the trouble since you will have to carbonate further anyway.
Sidebar: the gas released by yeast is not pure CO2, and carbonating at the end of fermentation will likely mean a lot of weird additional flavors. I say weird because it might include good flavors too.
