In this case it was a leaking cooling tube leaking the water used as a coolant.

>I am pretty sure the article gets this wrong.

It seems pretty accurate to me

>It is not that there were several liters of water (which would drown anyone immediately).

It filled slowly, and was concentrated around the back of his head. As it was in zero G it wouldn't behave like one might instinctively assume.

>It is that without adequate absorptive material (headband, chinblock) and proper ventilation, the moisture from exhalation just sheets over all internal surface in microgravity.

The visors even have anti-fogging surface coating (earlier suspected of being the reason the water tasted weird) - they're pretty impressive. The amount of moisture exhaled wouldn't account for the water present in the incident.

He definitely was in danger of drowning due to the litres of water sloshing about in his helmet. Luckily he kept calm (being a test pilot astronaut will probably help with that), as he couldn't even talk towards the end, and had to rely on hand squeezing to communicate. That's about as close to game over as you can get!