Yes, a lot of CS is mathematics (and EE), but it is not just that.
There is a notion of experimentation in pure CS, because CS asks the question, what can be computed on physical machines. And to check that, you actually need to build and check.
Nothing illustrates this better than Quantum Computing. Computer Science (and Physics) theories predict the existence of quantum computing, and suggest a computational advantage, but we will never know unless we build QCs and experiment.
There is a notion of experimentation in pure CS, because CS asks the question, what can be computed on physical machines. And to check that, you actually need to build and check.
Nothing illustrates this better than Quantum Computing. Computer Science (and Physics) theories predict the existence of quantum computing, and suggest a computational advantage, but we will never know unless we build QCs and experiment.