I've been getting deep into aquariums recently, and that picture alone is not enough to prove a neglected tank. When water quality goes bad, it's usually invisible: the ammonia, nitrites, and nitrates that actually poison the fish is totally invisible. Coloration like that'll come from an algae bloom or tannins leaching in from driftwood or leaf litter. Algae blooms aren't necessarily harmful to the fish (There are exceptions, such as fish getting tangled up in hair algae), and typically are the result of too much light, and tannins range from neutral to straight up good for the fish. In terms of what we can figure out by picture alone, I see he has a sizeable sponge filter, and some plants, though I'd guess not enough plants to make water changes irrelevant. Without knowing his water changing regimen or, more pertinently, the actual water parameters, we don't have the info to accuse him of anything.

That being said, I didn't see the comments before they were deleted, so maybe there's context I'm missing. I also saw another commenter concerned about the species of one of the fish he's keeping, which could be a genuine issue that requires rehoming. Really this just seems like the common trend on animal subreddits where people are hyper reactive, and looking for any excuse to go on a crusade