It is energy from nothing, but it is not a new type of energy. We knew about it before, just nobody though it can be harvested.
https://www.youtube.com/watch?v=J3xLuZNKhlY
Quantum Vacuum is real. In the "empty space", virtual particles [quark and gluon field fluctuations] of very very very low energy state are created and destroyed all the time, so fast that they don't have time to interact with almost anything. In this drive however, they are redirected to "flow" into certain direction while they are "alive", and some of them hit the specific wall of the engine. Because they hit that wall and not any other wall [they pop out from existence before they can do so], engine gets thrust.
That's the theory at least, there is still no concrete verified proof.
It so reads like science fiction, more so than anything I've ever seen.