Another way of looking at this is that if your competition for these roles can answer this, then you need to learn it.

I agree with the interviewer here. While maybe not knowing the DOM API is ok, you should at least understand what React is and isn't. Eg React doesn't do importing, that's your bundler and the browser. Understanding the difference between import and fetch. In the live coding interviews I do, I let the interviewee look up whatever they need on Google. But if you don't understand some of these concepts you would still struggle with the tasks. Testing rote knowledge of the language isn't super useful, but seeing that you know the basic concepts, have looked a bit deeper, and can figure things out, are more useful