I think he's right, it would be steam, because it releases energy, exothermic reaction, it would only turn to water if you removed this heat... but when you heat things they expand, so it would go counter to your implosion suction... I don't understand the german in the videos.
Anyway, test the theory and see if you could make something like that work
I do agree that the exothermic energy released will most likely heat the created water-molecules so much that they will (probably) convert to steam.
One would have to calculate to get the temperature and state of matter the water/steam is in, this is important to know the density of the created steam. On the other hand it's possible that the enthalpy of the gas is given off to the outside and the steam is quickly converted into water again.
The video shows the following: A HHO generator is plugged into the top connection of the reactor chamber, the bottom connection is connected to the water reservoir seen. there are two valves above and beneath the reactor which can be closed and opened.
The reactor has a cable which creates a spark to ignite the HHO mix.
In the first video they ignite the HHO (top valve is open) and see what happens: The water is is sucked into the reaction chamber, the result of underpressure in the chamber after the reaction. They try different versions with valves closed, open, ... In the third video they test different hose diameters and watch how long it takes for the water to go into the reaction chamber.