Is subtype polymorphism a kind of ad hoc polymorphism?

Question

"Ad-hoc polymorphism is obtained when a function works, or appears to work, on several different types (which may not exhibit a common structure) and may behave in unrelated ways for each type." – Strachey 1967

Subtype polymorphism seems to fit this description, albeit usually with late binding on the type that dictates the function's behavior. In Java, for example, the toString function works on any object at all, but has many wholly distinct implementations which are distinguished from one another based on the runtime type of the object; i.e., any class can override it and create a new ad hoc definition.

But when I poke around online, I usually find people making a sharp distinction between subtype polymorphism and ad hoc polymorphism; they are treated as wholly different beasts. Would it be correct to say that subtype polymorphism is a kind of ad hoc polymorphism? If not, why not?