Reading again the paper above, I see they referenced a paper by Szpak, et, al from 1998 (Fusion Tech. 33 (1998) 38). AN umarked copy of it is here: lenr-canr.org/acrobat/SzpakSonthebehavc.pdf They show how they measure evolved gases and it *IS* as I thought. They route the gases through a recombiner to make water and then collect the liquid water.
That was a very different experiment, and what techniques were used there may not apply at all. If we needed to know, we'd ask the researchers.