You're asking why units seen from a video made in 2011, long, long before a major redesign of the game was done to move it from all air units to air, naval and ground - are not seen in the game? That wasn't even a GAMEPLAY video, it was a 30-second trailer. It's not even the same engine! Later videos which had gameplay were done on the Divinity 2 engine, they were using character models taken from Divinity 2.
There have been videos released THIS YEAR which have had different graphics and different building models. Things change over the course of development. This is not unusual in any way.