What does it mean if a guy is always calling you while driving?

yeah..I know! it's very risky! cellphone while driving...But he told me that he's just being bored on a long drive from school...And I don't want to be his boredom reliever. But why is this HS guy friend of mine is always always calling me while he's driving although we're very very miles apart. But just every other Fridays not all the time. And it's been two years since we graduated and we're not really that close friends before. He told me before that I can call him whenever I'm bored. But I didn't call, just a return call. That's why he's always the one calling me. Does it mean anything? I mean why not call his sister, dad, or any other girl friends, so why me?