Maybe the site wasn't down, but you might have been unable to reach it.
This can occur when your internet service provider has a routing problem, making it impossible for you to reach their site.
In order for you to reach a website, the communication travels a couple of routers on the internet to the ip address of the webserver of the website.
If their is a problem on a hop, and there is no alternative route towards the destination, you can experience this type of problem.
Other sites can be reachable at this moment, just try to see it as a certain part of the internet which is not reachable at a given time due to a technical problem.
I generally avoid temptation unless I can't resist it. - Mae West