The command lists the EBS snapshots available for you to mount. Just like with VM images (AMIs), Amazon allows customers (and of course themselves) to make EBS snapshots "public" in order to allow other people to use them.

Here is an example: http://aws.amazon.com/publicdatasets/

So when the author says "My EBS Snapshot account was filled with hundreds of snapshots" that is technically not accurate. The output was of things strictly in his account as well as all the public ones available for use.

Some of those were marked public by the owners when they should not have been.