SpaceX First Stage Landing as Seen from the Barge

Why is this not on SpaceX' youtube, vine, twitter, or elon musk's twitter, and instead anonymous and with no details on that site?

Probably because it's a leak and they didn't intend to release it yet.

Wow were they ever close to landing! Completely amazing.

Did one of the legs break on landing, causing the rocket to fall over? Or did the leg break while the rocket was falling?

The stage had lateral velocity when it landed plus it came down at an angle, so one or two legs took all the energy of the impact and collapsed.

They are not designed to support a beating like that.