Having the type be inferred is precisely what omitting a type declaration does in a static language. From the point of view of a pedantic type systems theorist, Python is like having a static language where every variable has the the same type, "Object".
Anyway, they are talking about documentation. Many people think that having to peek inside a function to know what it returns is worse than having a compiler-checked type declaration. In fact, in most languages with type inference there is still a strong convention to write full signatures for all top level functions, as a form of documentation (return type inference is left for lambdas)