This is certainly an assertion, given it's hard, bordering on impossible to to demonstrate that other humans think.
When I say thinking I mean things like planning to get a snack by pushing a chair in front of a counter to then jump up and open a cabinet and then even being ingenious enough to pretend not to have done it, even putting the chair back and hiding the snack if spotted. This is obviously not just "see snack get snack" reactive operation. What I think is debatable dogs may have are things like metacognition which I'd put under the consciousness umbrella. Even that I've seen examples, but I agree its much rarer.
Philosophy is also not about what we think is true, but what statements we can defend. Solipsism is a notoriously difficult position to attack, even if we do not subscribe to it.
The fashion in which they do it is recognized by Aristotle in Historia Animalium, as well as in Metaphysics and De Anima.
He also mentions it in passing in Nicomachean Ethics (III.ii)
> Choice, then, seems to be voluntary, but not the same thing as the voluntary; the latter extends more widely. For both children and the lower animals share in voluntary action, but not in choice, and acts done on the spur of the moment we describe as voluntary, but not as chosen.
* https://classics.mit.edu/Aristotle/nicomachaen.3.iii.html
> It seems that choosing is willing, but that the two terms are not identical, willing being the wider. For children and other animals have will, but not choice or purpose; and acts done upon the spur of the moment are said to be voluntary, but not to be done with deliberate purpose.
* https://standardebooks.org/ebooks/aristotle/nicomachean-ethi...
And I've read plenty of philosophy and engage with it just fine. I think it's perfectly fine to break apart the basic premises of something because you avoid wasting the time reading the conclusions.
And in fact my criticism is to the author, not to Aristotle or Plato, although I don't agree with all that I've read that they wrote they were much smarter than me. I just have been able to read way more than them.