So you can’t rely on the Or HaChaim? Maybe he knew the truth.

How would he know? Did he have a revelation from Elijah? I’m not inclined to believe things like that. This is his interpretation of verses, or of mystical sources, and in my view that doesn’t carry much weight.

If a person has free choice, then he can freely choose to be an animal. From here it follows that an animal also has free choice.

In other words, the whole idea of free choice is childish and is meant to satisfy the urge for pride. That and nothing else.

The question of how he would know—you could ask that, then, about everything he says in his commentary! If I believe his interpretation of some particular verse, then I should also believe his interpretation of this verse too, no?
Besides, we’re talking about the Or HaChaim, not some random rabbi playing around like a child, right?

That is indeed correct. I don’t accept anything he says just because he said it. I examine each of his interpretations on its own merits and accept what seems right to me (he has no formal authority, and when it comes to facts nobody has formal authority). So I don’t “believe” any of his interpretations of any verse. At most, I study his interpretation and examine whether it seems plausible to me. Here I think he had no way of knowing this. He probably had one interpretive consideration or another, or he was influenced by the views common in his time (like all of us), but I’m not obligated to accept that. I too tend to think that animals do not have free choice, but I’m aware that this is influenced by what people around me generally think.
Of course I’m not claiming that he was consciously lying, Heaven forbid. He reached some conclusion and he himself truly believed it. So what? I’m not required to accept it.

Oded Kotler’s remark about the Knesset members from the Likud party is well known:

“30 seats, followed by a herd of animals chewing straw and chaff.”

That means a third of the Israeli Knesset entered parliament because of the “right to vote” at the ballot box of the animals, so clearly animals have choice.

He could just as well have said it about Arabs.
And the Haredim say it about the secular.
So there is certainly proof of it.

I seem to remember that in the introduction to Or HaChaim he writes that one should accept the most plausible interpretation of a verse even if it goes against the Sages of blessed memory. So here we have testimony from Or HaChaim himself that he would not have wanted us to “believe” his interpretation.
In several places he disagrees with the Sages of blessed memory’s interpretation of verses and writes, “And like a hammer that shatters…”