The author knew there was a problem, knew where the problem was, and knew what the problem was, but even with that and an extensive perusal of the standard he still only thinks he knows what part of the standard was violated, presumably because nothing else fit ("didn't explicitly say anything about invalid _Bool values. After some more searching, I believe I've found my answer"). There's no way anyone without omniscience could have predicted this obscure issue being present somewhere in Doom's 60,000 lines of code.

Specifically, there are responsible disclosure guidelines that came about to deal with the problem of people dropping 0day on a vendor with no prior warning. So the 90 days is a commonly-accepted amount of time to give a vendor to produce a fix. If the vendor needs more time they can request that the submitter give them an extension, although in this case it appears the vendor never responded, thus the repeated entries in the timeline saying "tried to contact vendor, no response" to show they tried to do the right thing.