Does their blocking of social media sites have anything to do with Bitcoin? E.g., where there posts about Bitcoin that were the trigger for the block/ban decision?

It's important that we not jump to conclusions, and you haven't provided a source of your information so I want to make sure we don't get worked up over something that we know little about.

If any government banned bitcoin it would only apply to how their residents or citizens used Bitcoin. It may not apply to ownership, but for use as a transaction medium within their borders. And anyone who's been involved with Bitcoin over the last year knows that its use as a currency is being replaced with its use as an investment asset. In any event, Sri Lanka can't take down Bitcoin - it exists beyond their borders!