A mark on a stick can encode an infinite amount of information. That doesn’t make it a computer.
Yeah it does. Why not? A computer is essentially just a system of inputs and connected levers. How much do you know about stuff like kernel code or writing computer programs?
Couldn’t you write something that looks a whole lot like a very logical code on your stick, and use it to analyse a maths problem? What if you wanted to perform a task like multiplication by hand?