To me, intellectual curiosity is basically "learning for the sake of learning". In other words, picking up a skill or researching a topic that interests you without having a real need to apply said skil/knowledge professionally or personally.

Often the research may be tangentially related to their work, but it doesn't have to be in order to be 'credited' as intellectual curiosity.

Outside of CS, demonstrating curiosity can be almost anything. A non-CS person learning a technical topic is actually a decent example. Non-programmers that buy Arduino and do some home automation project.

It can be almost anything I'd think. Many people don't dedicate much personal time to learning. Demonstrating that learning can be challenging.

I have clients that require interviewees to do a presentation on anything at all during the hiring process (both non-tech and tech employees). Some have demonstrated game strategies they've studied.