I'd certainly say that it is, it certainly meets the dynamic binding pre requisite. And small talk certainly does, so why does Objective-C not qualify?
Many languages have static subsets. For example, many languages won't let you change the meaning of `1+1` while others might allow you to dispatch the addition dynamically.
In fact, a static subset is a very nice property to have in a dynamic language. It's probably the easiest way to make a dynamic language self-hosting. For instance, PyPy uses a static subset of Python called RPython and Squeak uses a subset of Smalltalk called Slang.