How one socializes within their family isn't necessarily appropriate for how one socializes outside of the family. People interact differently, additional social skills are needed such as learning how to introduce oneself, gain the trust of others, gauge when to trust others, know when / when not to offer personal information, and when to just walk away among other things.
If someone spends the mass majority of their time at home they often don't develop the outside the home social skills until such time as they're forced to do so...and then it can be a painfully bumpy ride in a short time span. Is this true in all cases? Of course not, it's just my personal experience that it happens more often with those who are home schooled as they often have less social interaction during their school age years. Your personal experience of course may vary.
