If I can know the types from just looking at the code then it must have adequate type annotations and none of this matters

That’s not really true. It depends on the language. In Rust, it’s common to read a function without any explicit types except for the arguments and return type. So you may not know what types are used in the body without referring to the signatures of functions called.

If I can’t tell the types and I have to pull the code locally to figure it out then I’m not starting the review on a good foot.

It’s rare that knowing the types is critical to actually reviewing the code. Types are mostly for the compiler to help you. When reading the code, it’s more important that you see idioms, descriptive names, and test cases. There are rare occasions where it’s necessary to determine a type to resolve some ambiguity in how the code works, and in those cases, there are tools to help you do this (usually the same tools you use while writing code, e.g. LSP editor plugins and grep).

I think people here are thinking about type inference in a very local scope and not at a public function level which I understood the author to be complaining about.

In my very first comment, I said I can’t comment on OCaml. I am only really speaking on Rust here, where you have local inference and mandatory function type signatures.