If your friend's employer truly wanted him to start a new project in the past 2-3 years in AngularJs, he did the right thing. That tool is no longer supported, and companies starting new projects in it have no idea what they are doing.

However, if it was Angular, your friend is a fool. React will not last forever--no tool does. And here he had this company offering to pay him to learn a whole new way of working, to gain deep experience in it. Now, there's no way of knowing whether Angular will outlive React or vice versa, but you're never worse off for having more skills on your resume. I would agree that when it comes to your own personal time, you're better off going deep on a technology you already know than picking up a new technology (companies don't like to pay you to do something unless someone else has already paid you for it), but, heck, if a company will pay me to learn something new, I'm all in!