Most Helpful Guy
you never know. these questions are kind of hard to answer by someone that has no idea how that person really is. You should now better if it might mean something or not.
Did he post on his Facebook after you two split up and use Facebook as a tool to get a message around? What was your post about? If it was "love" related that might have got to him and he liked it so you can see it, so you can remember about him. Especially if you haven't talked since you've split up.
There are lots of things to consider. Did you recently see eachother? I had one girl that i bumped into the street after a year and she suddenly started to post on her Facebook things that i told her back in the days. (you can't get any clearer than that). But what i'm trying to say is: people use Facebook to send a message. Some do it consciously waiting for a reaction, some do it without realizing, but Facebook is more or less US.
Never mind those that say you might over think this. You can write books to describe people's behaviour over Facebook. So in my opinion, if this like was out of the blue, what you should think about is: could have the message you posted, spark something in his mind?
I wouldn't just like something of my ex's out of the blue, unless i wanted attention or missed her in some way.
Most Helpful Girl
I guess it probably means nothing. On my Facebook wall, sometimes there are posts like "X liked this picture in June 2014", "Y liked this status in April 2011" blah (X and Y are my friends). I don't know, maybe he found your post like that and clicked like?