Which is bullshit and absolutely none of their business.

And also not very enforceable in some areas. I got legal advice on this from my own attorney some 20 years ago. I had created a piece of software on the side while working under a contract that said something similar. The software took off and I was worried about it. He advised me that worst case would be paying the company the money I earned while under that contract, but even that was a stretch.

In addition to being bullshit it is also a hint you should be moving on.