I agree with bebanjo. Kids are all different, and drawing conclusions about home education based on the one or two children they have met is not really right, is it? if I had only ever met a couple of schoolchildren and they had poor social skills, it wouldn't be fair of me to conclude that all schoolchildren were like that and that school had made them that way.
There's another point, which is that home educated kids are a self-selected (or parent-selected) group. By virtue of that it seems probable that they are not representative of the larger population. Those home educated children your friends met, who struggled to adapt to school and who didn't swim easily in a large pool of children - is it not possible that the children have always been like this, always will be like this, and that that is the very reason their parents chose to HE in the first place?
Take one of my kids, for example. She doesn't do school-type things well. Her attention span is very short. She dislikes being told how to spend her time. She isn't like other kids her age. She is several years behind her age peers academically. Because she has a genetic condition which is known to affect brain development, I can confidently assert that home education isn't solely responsible for all of her differences. It's the other way round: her differences are one of the reasons WHY she is being home educated. Some genius glancing at her in the school corridor might easily jump to the wrong conclusions, believing that home education had damaged her socially and academically.
My dd has an indisputable diagnosis, but for most it isn't so clear. I've known any number of kids whose parents recognised early on that they weren't cut out for the school system: too active, too anxious, too solitary, too bright, not bright enough. Maybe it's true that a disproportionate number of home ed children have difficulty when they do later go to school. Even if true, it doesn't mean home education caused the problems.