From 3:30 to around 3:45 in that video you can clearly see players fighting AI Satyr type enemies from the singleplayer. In the first snippet (3:36) there are two different coloured players not attmpting to fight at all, so it is the muliplayer.
In similar videos we have already seen the spear revealed as the other weapon type (along with the Leonidas pre order bonus).
This footage is backed up by Papy stating they would look into a Horde Mode (but no promises) in an earlier interview
Perhaps this mode was tested and cut, but I believe it will be the final mode and am looking forward to it. I enjoy good horde modes, especially ones with higher difficulties that require you to work as team to survive.
Apologies if this has already been posted.