Like I said, it depends very much on how you define computer. To me "processing information" == "computation". And a physical system that performs "computations" is a computer. Therefore, a brain is just one type of biological computer.

In a computer science class, the first thing they should teach is that the word "computer" in the course name is abstract, and not just about the metal slab on your desk. There are fundamental laws that apply to all information processing systems, whether electrical, mechanical, or biological. So it makes sense to put them in the same category at times.

But obviously words mean different things in different contexts, and "computer" might mean something entirely different to a neuroscientist than a computer scientist. But I don't think a neuroscientist would disagree that a brain is a computer using the loose definition I described above