What do explicit mutation and static mental model mean?

In this article https://medium.com/@dan_abramov/youre-missing-the-point-of-react-a20e34a51e1a I read the quote "React’s true strengths: composition, unidirectional data flow, freedom from DSLs, explicit mutation and static mental model." at the very end.

What do explicit mutation and static mental model mean?

Thanks!