You don't know what you're talking about, you're just speculating.
The kids I worked with went to specialized classes anywhere from 1 to 4 days a week (where I taught them), had a network of active social relationships, participated in local sports clubs, and were also able to avoid some of the pitfalls of traditional schooling. They learned from some of the best teachers around for the subjects their parents didn't feel comfortable with. They were commonly more well-adjusted people than most. They are people you wouldn't guess were homeschooled and they went off to standard (and sometimes elite) colleges. You may know a lot more homeschooled people than you realize.
I also saw some real problem kids where parents were not doing the necessary things to give the kids space, independence, and proper socialization. In my case, that was the exception but obviously I didn't get to see any of the kids who are so isolated that they wouldn't have come to the out-of-home classes where I was a teacher.
To assume that homeschooling means the kids never get out in the world, don't have friends and social interactions and are just cooped up inside just shows you have no understanding of what homeschooling is like (in that it varies widely). Just like all other forms of schooling, it can be done wonderfully and done terribly.
You have no understanding of what the case is for this particular parent.