Didn't that make a mockery of all the "many eyes" arguments oft touted in favor of Open Source?
Nope. Once the bug was noticed it was fixed very quickly: i.e. it was a shallow bug. If you think than phrase means OSS is bug free, you have misunderstood it.
The quote is often misunderstood, its hyperbole. It illustrates a point nicely but in reality few users are developers and few developers are qualified readers.
More importantly the bug was not discovered by eyeballs on source code. The techniques used seem to be the same applied to proprietary closed source code. They were testing the binary.
"“We developed a product called Safeguard, which automatically tests things like encryption and authentication,” Chartier said. “We started testing the product on our own infrastructure, which uses Open SSL. And that’s how we found the bug.”"