"Been reading a bit about the Nestorians, and find it kind of funny that Nestor himself probably wasn't one."
The same has been said about Pelagius. With Nestorius, however, it is a fact that he argued against the title of Theotokos for for the Virgin Mary, asserting that she should be called the Christotokos, which of course is pretty much definitional of the heresy itself.
Which did spark the whole debate, you are correct. I think Harold Brown (the author of the book) was saying that while he did coin the term Christotokos, he did not want to separate the Divine and Human natures of Christ into two separate persons. But from this distance of time, it is hard to say for sure if Nestor's later statements were mearly trying to "make up" or not.