Only for people who don't actually understand what it is and how it works. Which seems to be a problem, everywhere.
I think that, as you have described it, it sounds like avoidance. But "everything is an illusion" can be a very important, foundational idea in Buddhism.
Yeah...sounds like he has grasped onto that as an answer for whatever he is going through. If he is in or was in a cult, that will also probably be something the leader has instilled in the followers.
So, do you expect him to accept what you say? Because if you do, I think you'll be *very* disappointed. Can you talk to him without any expectations?
This. And "illusion" in Buddhism doesn't really mean "not real;" it's more of a "things aren't as they appear."
People--and, I suspect, those in cults esp.--take a phrase they hear repeated and put their own spin on it. Or the interpretation given them by the leader.