Could intentonality be an illusion? Of course not. But seemingly intelligent people think otherwise:
A single still photograph doesn't convey movement the way a motion picture does. Watching a sequence of slightly different photos one photo per hour, or per minute, or even one every 6 seconds won't do it either. But looking at the right sequence of still pictures succeeding each other every one-twentieth of a second produces the illusion that the images in each still photo are moving. Increasing the rate enhances the illusion, though beyond a certain rate the illusion gets no better for creatures like us. But it's still an illusion. There is noting to it but the succession of still pictures. That's how movies perpetrate their illusion. The large set of still pictures is organized together in a way that produces in creatures like us the illusion that the images are moving. In creatures with different brains and eyes, ones that work faster, the trick might not work. In ones that work slower, changing the still pictures at the rate of one every hour (as in time-lapse photography) could work. But there is no movement of any of the images in any of the pictures, nor does anything move from one photo onto the next. Of course, the projector is moving, and the photons are moving, and the actors were moving. But all the movement that the movie watcher detects is in the eye of the beholder. That is why the movement is illusory.
The notion that thoughts are about stuff is illusory in roughly the same way. Think of each input/output neural circuit as a single still photo. Now, put together a huge number of input/output circuits in the right way. None of them is about anything; each is just an input/output circuit firing or not. But when they act together, they "project" the illusion that there are thoughts about stuff. They do that through the behavior and the conscious experience (if any) that they produce. (Alex Rosenberg, The Atheists' Guide to Reality: Enjoying Life Without Illusions. The quotation was copied from here.)
Rosenberg is not saying, as an emergentist might, that the synergy of sufficiently many neural circuits gives rise to genuine object-directed thoughts. He is saying something far worse, something literally nonsensical, namely, that the object-directed thought that thoughts are object-directed is an illusion. The absurdity of Rosenberg's position can be seen as follows.
1. Either the words "The notion that thoughts are about stuff is illusory" express a thought -- the thought that there are no object-directed thoughts -- or they do not.
2. If the latter, then the words are meaningless.
3. If the former, then the thought is either true or false.
4. If the thought is true, then there there are no object-directed thoughts, including the one expressed by Rosenberg's words, and so his words are once again meaningless.
5. If the thought is false, then there are object-directed thoughts, and Rosenberg's claim is false.
6. Rosenberg's claim is either meaningless or false. His position is self-refuting.
As for the analogy, it is perfectly hopeless, presupposing as it does genuine intrinsic intentionality. If I am watching a movie of a man running, then I am under an illusion in that there is nothing moving on the movie screen: there is just a series of stills. But the experience I am undergoing is a perfectly good experience that exhibits genuine intrinsic intentionality: it is a visual experiencing of a man running, or to be perfectly punctilious about it: a visual experiencing AS OF a man running. Whether or not the man depicted exists, as would be the case if the movie were a newsreel, the experience exists, and so cannot be illusory.
To understand the analogy one must understand that there are intentional experiences, experiences that take an accusative. But if you understand that, then you ought to be able to understand that the analogy cannot be used to render intelligible how it might that it is illusory that there are intentional experiences.
What alone remains of interest here is how a seemingly intelligent fellow could adopt a position so manifestly absurd. I suspect the answer is that he has stupefied himself by his blind adherence to scientistic/naturalistic ideology.