Carlini said "hundreds" of crashes, not 1000+.
It's not that only 5 were true positives and the rest were false positives. 5 were true positives and Carlini doesn't have bandwidth to review the rest. Presumably he's reviewed more than 5 and some were not worth reporting, but we don't know what that number is. It's almost certainly not hundreds.
Keep in mind that Carlini's not a dedicated security engineer for Linux. He's seeing what's possible with LLMs and his team is simultaneously exploring the Linux kernel, Firefox,[0] GhostScript, OpenSC,[1] and probably lots of others that they can't disclose because they're not yet fixed.