Well, they heat it up, maybe not to boiling, but enough to create steam...
From the article:
Water from one side is heated and allows water vapor to pass through the membrane, which is then condensed on the other side.
Doesn’t say anything about steam.
You made that up.
The latent heat of vaporization does not change regardless of temperature the water is when it goes to a vapor state.
I suspect we are missing something that the article does not explain.
One version of vacuum flash evaporation requires pumping to lower the pressure, depress the boiling point. The other point is to raise the pressure of the outflow product stream to enable condensation. The heat should be recycled from the condensate outlet to inlet to prevent ice formation at the boiler/evaporator.