That’s hard to say. It might be a few years’ supply for a large pool and due to the shipping costs it made more sense to get this amount. 330 gal isn’t all that much really (an Olympic sized pool is 660 000 gal for example). Some articles I’ve seen for this story use a tanker truck picture which is crazy misleading as it’s more like one of these tanks which I often see in multiples in the back of a 1-ton pickup.
This isn’t like the P Diddy baby oil where it was a crazy weird amount with no other purpose than something freaky. The acid alone isn’t necessarily evidence of anything nefarious or newsworthy; people just watch breaking bad so think acid is only for dissolving bodies or something, and the news sites feed into that to get clicks. Just offering up calorie-free content instead of anything of actual substance.
Now, if there was evidence they used the acid for something bad? Then that’s something.
Desalination is a good explanation too. The point really, is that just ordering certain chemicals in bulk isn’t necessarily shady even if they sound scary.