There are many abstract concepts that need to be realized before we can usefully call a particular device a 'computer'. Many, but certainly not all, of these, are gathered up into things like Turing Completeness, Von Neumann Architecture, etc. On that (admittedly mostly theoretical) scale, it is meaningful to discuss computers as a broad class having certain characteristics. That's what allows us to reason effectively about things like efficiency and correctness in computer algorithms. They even allow us to meaningfully compare digital, analog, mechanical and quantum computers, despite radical differences in the physical hardware. If the object you're showing me doesn't support conditional behaviour ('if' statements), it's going to be pretty hard to convince me to discuss it as though it were a computer.