Why has he blocked me on Facebook chat?

I got a weird message from this guy and asked him about it, he claimed it wasn't from him and was going to find out who it was from. I knew of him but didn't know him personally (also heard that he might be interested in me). After trying to solve the mystery message we became Facebook friends but didn't didn't interact at all after that. I would see him on my chat list all the time. Recently (about 4 months of being Facebook friends) I see that I have been "blocked" and can't see when he's online. I can see when he was last active and shows in increments of 30 seconds, 1 minute etc. So I know he's on.

Why would he block me?
Why has he blocked me on Facebook chat?
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