Maybe, maybe not. I used to teach 9th grade, which is a tricky age. I taught quite a few kids who had been in private school or had been homeschooled all their lives, and then had been moved to public school for their high school years.
You may agree or disagree, but many parents see that as the "ideal" year to make a move because EVERYONE is new to the school, so their kid has a good chance of fitting in easily, and many people want the large-school environment, where we offer multiple AP courses, 4 languages, sports, clubs . . . and other opportunities that're difficult to provide on your own. I remember two girls who left their small Christian school and transferred to public school their senior year SPECIFICALLY BECAUSE they wanted to be able to attend prom; I don't think I would've made a move for the sake of one evening. Anyway -- I digress -- but the point is that 9th grade teachers tend to see their share of "newbies" to the public school environment.
Thinking back over the years, it was kind of split 50-50 between those who came in socially ready and those who were just lost in what they saw as a big, unmanageable social system.
Those who fit in well don't really stand out in my mind -- they might've required a bit of time to acclimate to their new environment (as do all 9th graders), but they were fine after a few weeks of learning their way around. Those who didn't, I remember well. Sometimes it's little things like the girl who simply WOULD NOT accept that she couldn't write in her textbooks -- her mom told her to do whatever she pleased, and she paid for the expensive textbooks at the end of the year (great lesson for the kid, huh?). Other times it's big things like the kid who wouldn't talk to other students, even when placed in a group and assigned a specific job for that day's assignment. And I remember the girl who attended ONE CLASS on the first day of school and called her mom in tears saying, "I just can't do this". And I remember one outspoken student who shared her firm opinion that slavery was a fine institution that should be reinstated; she clearly had no idea that she was offending many people in the classroom, nor did she have any sense of self-preservation.
Obviously, I don't know how their parents raised them and what socialization opportunities they had prior to 9th grade, but it's pretty obvious to me that SOME homeschoolers DO miss out on great amounts of social skills. So I wouldn't say, "Oh, this isn't a concern at all. Just blow it off." Instead, I'd say that if you're going to homeschool you need to actively seek out opportunities for your child to be involved in activities with kids their own age.