> given that there aren't obvious word order patterns across languages, how does the human brain do so well at learning the rules that are a peculiarity to any one of them?

That simply means there are rules at a deeper level in the brain, and they may crystallize this way, or that way, depending on the particular language.

The study, if correct, simply says the rules are not apparent at the outermost level. Well, dig deeper, go closer to the hardware, and at some level the universal order should appear again.

After all, my neurons don't work any different than your neurons. But I suspect the highest level where universal rules operate is higher than that.