The original commenter offered his story as an issue with Ruby preventing X.
The 20/20 hindsight is not meant to retroactively solve their problem, it's mean as a counter-argument, that the problem was their design, not Ruby.
The posters point is that Ruby has surprising concurrency semantics compared to other solutions.
It has the same concurrency semantics w/r/t IO as any other language that isn't using an event based runtime. If you wrote your app in C and used a single thread you'd have the exact same issue.