It sure isn't a good sign. Think back about what you messaged to him previously. Something isn't right. Try to learn from this and don't take it so seriously. You have to move on.
Do you do stupid things or ask him lame questions when he's on? Or nag him? If you know him in real life, you can ask. Otherwise you're doing something, seems like too much of a coincidence.
As far as I'm concerned, it means he doesn't want to talk to you. It sounds harsh but if he doesn't even have the courtesy to say hello, then maybe he isn't such a great guy anyway.
