"pure FP" does not mean only writing in a functional style. Purity refers to referential transparency, ie., functions do not depend on or modify some global state.
I know what purity is. It is a core principle of functional programing. So ”functional“ already implies purity, and ”pure functional“ implies exclusively functional (e.g. Haskell).
Neither of those are true. He does more FP ”where reasonable“, and that decreases the need for inlining. He does not do pure FP, and he still inlines.