That would align with the curl feedback you linked, they aren't using mythos but are finding bugs with other models. Presumably the expectation would be that with mythos they'd find more that were missed by other models already used.
It's not quite apples-to-apples. It was Opus on Firefox 148, Mythos on 150. A better test of Mythos vs Opus would have been to apply Mythos to Firefox 148. Or also re-apply Opus to Firefox 150.
Do we know all the Opus+Firefox 148 bugs are fixed in Firefox 150? Do we know the number of new bugs introduced per Firefox release?
That may be parsable from their bug tracker, though I don't know of all bugs raised by mythos are public.
I'd be particularly interested in how many of the bugs found existed in 148. Assuming most or all of them weren't newly created bugs added in 149 or 150, the comparison should still hold even though Opus and Mythos looked at different releases.