I would say he misses a big point on the hard bugs though. Saying something is proprietary does not mean it makes enough money to hire such high caliber professionals, on the contrary.

I have worked with a lot of extremely competent developers on open source, but my experience with proprietary software was quite the opposite: professionals are untrained (to the point where they can't even use versioning properly) and would be incapable of finding such bugs anyway.

Now assuming that a proprietary cryptocurrency has the resources to hire a respectable audit firm... it is more far fetched than assuming that such star developers will just work on an open source one for fun.