The employer probably wanted to talk to him about it, to decide whether there really was enough similar tech (or even shared code) that it might harm the compan

The employer probably wanted to talk to him about it, to decide whether there really was enough similar tech (or even shared code) that it might harm the company. That's basic due diligence. Probably after going over it, they determined that it would present no harm. Notice that this was not a legal process, just an employer and developer communicating.