and it's different from 50 randomly selected true coin tosses because you think it's impossible for all of them to alternate?

I understand your point, but the context is that repeatedly, experiments have shown that humans inject too much pattern to be good rngs. It turns out that is visible with training after the fact.

Yes, it is possible that any two 50-sequence patterns are actual rng. But some of them are much more likely, and we can tell.