For anyone who didn't read article: this was an electric motor being tested on one side of the aircraft, with the other being a conventional turbine engine aka turboprop. The electric motor was fed by electricity generated in a fuel cell that used hydrogen as the fuel source. In other words, they didn't "burn" the hydrogen in a turbine engine, This is why the pilot reported it was so much smoother. It was an electric motor. The hydrogen was sourced from water, not from natural gas so was in some sense truly "green"