dotadotadotadotadotadotadotadotadotadotadotadotadotadota DOTA!
read like nanananananananananananananananananana Batman (if you remeber the origan batman theme)
That movie uses ingame models/assets with additional animations. Just like they did with the Team Fotress 2 movies. That's how far the source engine has come, with the artstyle of the environments it looks like a real "cartoon". For instance the reflections of the river matches that of the leaked screenshot.
Diablo3 did the same with their demon hunter movie, it just didn't look as good.