I combed through the article and a previous article linked in it, but I can't find any concrete answer one way or the other. My intuition is that it would have to be recalculating it's inputs as the environmental variables change. They could have modeled in expected tire friction coefficient changes, or perhaps the task is more forgiving of that changing variable than I expected.

One of their stated goals is to drift in tandem with another human driven vehicle though, so they are likely aiming for complete, adaptable autonomy.