I don't know how to verify it, but I've been told that drinking seawater is acceptable to do and is just enough to keep you alive.

If I were to do it though, I would invest in some water filters which are fairly cheap and can remove a lot of things that you wouldn't want to be drinking.

This is false. Sea water is >3% salt and human kidneys can't produce urine with that much salinity or greater. Since they need more water to extract that much salt, the net effect is dehydration. This rower probably had a desalination machine, or just a big reservoir of fresh water.

(Though there might be some obscure edge case, and if you're about to die of dehydration that a little bit of seawater will buy you a minuscule amount of more time? doubt it)

I recall one article mentioning that there's desalination gear on board (that's what the solar panel is for?)