I think the newish thing is traits such as in Rust.
Of course, there is some object-orientedness to it, the author even calls part of his new code "objects". I guess some people would call that OOP, but it's certainly not traditional OOP.
Rust does a really nice job of making that the first obvious thing to reach for (simple structs, traits and generics), and making the slower stuff like dyn traits (v-table indirection) more annoying and less desired. Reducing indirection and abstractions makes it easier to reason about code.
> Normally, I would probably not make these member functions, but since The Witness is a more C++-ish codebase than my own, I thought it was more consistent with the style (and I don’t have a strong preference either way)
My interpretation of this is that normally he'd make plain C structs and functions that operate on them. So quite far from anything people would normally describe or think of as object oriented.