It's not, it's an ultra-processed food, because you can't just eat mechanically separated chicken, it has to be made into a paste, a goo, to become edible.
So, in food production you can't just "make a paste". A lot of chemical stuff begins to happen very quickly. Oxidation being a major one, with separation being another.
How do we mitigate these issues? We add things. We'll add emulsifying agents, de-clumping agents, things to retain moisture, other things to retain color(or just treat it with gasses, or dye it), etc etc.
While it's easy to say "they're just making a paste", in reality that is not what's actually being done.
That said, there are plenty of mechanically processed foods that are fine but fall under the "processed" headline because they're technically processed.
The devil is in the details though and people really need to get educated on basic food processing/preparation. I don't mean raw milk or grass-fed carnivore Idiocracy, but even a basic understanding of what a preservative is would be helpful.