Try not to compare your son and daughter on this. They may just have fundamentally different personalities. And he may not get invited on play dates because the other boys his age are all involved in sports teams that eat all of every weekend and most weekday afternoons as well. But a; boy does not have to be in sports to have his own interests and friends.
You didn't mention some things that would help us a lot in responding to this question.
What IS he interested in or involved in? For instance: Is he very academic and is reading a lot at home (which is great!)? Is he currently involved in any group activities or classes outside school, such as a sport or a martial arts class? Does he have any outside activities of his own, and I'm including at-home, quiet activities here -- such as reading, writing, making models, craft stuff, hanging out outdoors even alone, etc.? What does he do with the time at home--watch TV or play computer games on his own? He might need to find something that engages him, and that might mean helping him find it. He won't know to go to the county parks and rec catalog to seek out courses or activities, or to ask at the community center, so you can help him out and offer him options.
If he does have some other interests, whatever they may be, I think he's probably doing OK. But if he does nothing much -- have you tried asking him if he would like to take a class (anything! woodworking for kids, which does exist, or cooking or fencing or basketball or dance or...whatever). If he is not a team sports kind of guy, that is just fine. If he loves to read, would he like a book club at the local library? (Ours does book clubs for boys, to appeal especially to them--If you local library does not have one and you think he'd like it, go see the children's librarian there and volunteer to work with her to start one.)
He may not be having scads of pals over like his sister because (1) he is just a quieter, more introverted person, which is fine; (2) the guys his age that he knows do not share his interests, whatever those are; (3) he does not think to invite the guys who DO share his interests -- Does he for instance have teammates or pals in other activities, but you suggest only the names of school classmates?; (4) he is socially awkward.
The only one that would worry me would be number 4. Think about it: Does he come home from school but never talks about other kids at all? Does he seem to do school group projects (they should be having those by now) but never discusses his partners? Has the teacher mentioned that he seems to work solo a lot, or he doesn't seem to bond with other kids? Have you asked his teacher about whether he has friends at school that she notices? If the answer is no to all of those -- I'd press a bit harder about having acquaintaces over and I'd be sure at first to have a specific activity in mind so the boys are not just hanging out saying "Whadda you wanna do?" Tell him you have passes to go bowling and he can bring a friend. Or tell him you're going to take him to the movies and he can bring three friends and you'll all get pizza afterward. If he seems awkward, help him by initially arranging activities so all the boys have something to engage in and talk about even if they don't have a ton else in common yet.
There is a number 5 too. At 10 some kids just start the pre-teen moodiness and that can include a need for more down time and alone time. It's not odd, it's normal, unless they truly cut themselves off from others including family.