At 8:45 he mentions "a playable version of an old Dark Forces demo" included as bonus content, which I'm assuming is the "lost" level aboard a Star Destroyer? It is described in this FAQ:
Quote
8.5 What happened to the Imperial-class Star Destroyer Mission?
===============================================================
The DF box shows a Mission aboard an Imperial-class STD that doesn't appear
in the game. Daron Stinnett has this to say:
Originally, that was our first level. It was a really well designed
level, but we decided that it was too big for the first level of the
game. We were concerned that the puzzles were too difficult and that the
level was too non-linear for beginners. So instead we created the secret
imperial base. Much of the geometry for the Imperial-class Star Destroyer
was carried over to the Executor. But the mission was different, so not
all of the geometry could be reused.
===============================================================
The DF box shows a Mission aboard an Imperial-class STD that doesn't appear
in the game. Daron Stinnett has this to say:
Originally, that was our first level. It was a really well designed
level, but we decided that it was too big for the first level of the
game. We were concerned that the puzzles were too difficult and that the
level was too non-linear for beginners. So instead we created the secret
imperial base. Much of the geometry for the Imperial-class Star Destroyer
was carried over to the Executor. But the mission was different, so not
all of the geometry could be reused.