make clear that instanceof supertypes are not base types

Author: ginsbach

docs/codeql/ql-language-reference/types.rst

@@ -406,7 +406,9 @@ However, `foo_method` is not exposed in `Bar`, so the query `select any(Bar b).f
 results in a compile time error. Note from the example that it is still possible to access
 methods from instanceof supertypes from within the specialising class with the `super` keyword.
 
-Crucially, the base class methods are not just hidden. The extension relationship is severed.
+Crucially, the instanceof **supertypes** are not **base types**.
+This means that these supertypes do not participate in overriding, and any fields of such
+supertypes are not part of the new class.
 This has implications on method resolution when complex class hierarchies are involved.
 The following example demonstrates this.