These colleges are increasingly competitive. While some colleges probably do mean they are truly optional, I honestly think it’s a mistake not to take an interview if offered.
If he is admitted, there is an expectation that he will engage, not only with other students but also professors. There are so many kids who are shy, awkward, etc…, on the spectrum or not. If he’s ever planning to apply for research, or jobs, or get recommendations, or whatever, he’s going to need to talk to people. Now is a good time to get used to the idea.
Sure, he can practice, but interviews are supposed to be informational. They aren’t trying to embarrass kids or make them feel uncomfortable. They know kids are nervous, aren’t very experienced, and so forth. He really should interview if he can.