No, headphones don't make people antisocial. If someone is wearing headphones, respect their privacy and just leave them alone. Some people just don't like to chat to random people on the subway or at the supermarket. Some people just don't see the value of mundane conversations with strangers.
It depends on the culture and personality. Some people like it, some don't. In the US, people are more inclined to chat to strangers, and in Germany for example they aren't. These differences are actually what make us "human", so it's not a binary decision of: talking to strangers == good, and headphones == bad.