Please help me understand “Finding the Dynamic Type in a Generic Context”

Please help me understand this section!

I'm reading Finding the Dynamic Type in a Generic Context that has this snippet:

func printGenericInfo<T>(_ value: T) {
    let t = type(of: value)
    print("'\(value)' of type '\(t)'")
}

protocol P {}
extension String: P {}

let stringAsP: P = "Hello!"
printGenericInfo(stringAsP)
// 'Hello!' of type 'P'

... that's followed up by this sentence:

This unexpected result occurs because the call to type(of: value) inside printGenericInfo(_:) must return a metatype that is an instance of T.Type , but String.self (the expected dynamic type) is not an instance of P.Type (the concrete metatype of value).

1. How come String.self is not an instance of P when I can run this code?

func f(_ t: P.Type) { print("...") }

f(String.self)

2. Why does type(of:) return the concrete metatype outside but not inside generic functions?

print("'\(stringAsP)' of type '\(type(of: stringAsP))'")
// 'Hello!' of type 'String'