docs: clarify get_method_signature_hook fullname uses call-site class

mypy/plugin.py

@@ -647,7 +647,7 @@ def get_method_signature_hook(
         may infer a better type for the method. The hook is also called for special
         Python dunder methods except __init__ and __new__ (use get_function_hook to customize
         class instantiation). This function is called with the method full name using
-        the class where it was _defined_. For example, in this code:
+        the class of the object on which the method is called. For example, in this code:
 
             from lib import Special
 
@@ -663,7 +663,7 @@ class Derived(Base):
             x: Special
             y = x[0]
 
-        this method is called with '__main__.Base.method', and then with
+        this method is called with '__main__.Derived.method', and then with
         'lib.Special.__getitem__'.
         """
         return None
@@ -672,7 +672,7 @@ def get_method_hook(self, fullname: str) -> Callable[[MethodContext], Type] | No
         """Adjust return type of a method call.
 
         This is the same as get_function_hook(), but is called with the
-        method full name (again, using the class where the method is defined).
+        method full name (using the class of the object on which the method is called).
         """
         return None