Why can I assign to a concrete type that doesn't implement type-parameter interface bound of the returned type

Can someone help me understand why the code below compiles:

class Main {  
  public static void main(String args[]) { 
    Concrete c = foo();
  } 
  public static <T extends Interface> T foo() {
    return null;
  }
  interface Interface {}
  static class Concrete {}
}

In my mind, Concrete c = foo() should not compile since T is bound to Interface only and not guaranteed to be Concrete.

If I switch null to (T) new Interface() {} it sill compiles with unchecked warning (on the return expression inside foo(), not on Concrete c = foo()). Obviously it gives me a ClassCastException when executed.