This is a great explanation of why a man would send a random message:
He just want validation. It's not a good faith effort to talk or get back together. Do not respond to something so vague. He wants you to think about him, but he doesn't want responsibility for your feelings. And check out the bad advice from her friend: Say something to have closure. But did she get closure? No, she continues to think about him and there is no resolution. Look at the fucking mind games men play.