I "think" though, that the author would distinguish thinking in language from thinking by the use of language. Analogy: to move from room to room, one naturally and even subconsciously walks there. But in fact, there are many other ways to motivate one's body, to get to the next room. It is the "intentional state" of desiring to move, that causes, directs, integrates, and guides the motion.
He is saying that the basic process of thinking is by its nature, not a process of semiotics and tongue -- that thinking has more dimensions than linguistics and is a process of its own at the core.
"I think, therefore I..." use language.
To press the point further, I'm confident he is arguing for the human soul -- and doing a good job of it.
Moreover, much of what I think I would not have thought without language. The concepts of the US Constitution are not expressible without words. Judicial reasoning, at least traditionally sound judicial reasoning before left wing whiners took charge, is verbal reasoning.