Its a style called JDM, (Japanse Domestic Market) they are very large overstocked tanks with INSANE filtration. Some agree, others disagree but a quick search will find there has been many discussions on tanks like this on MFK over the years.
This guy is better at housing Pirarucu than a lot of other people that have purchased them so what is the problem...
Yes MFK has a lot of people who will flame about tank size, but those people need to learn that not EVERY set up is perminent. Most set ups aren't... my 225 when everything is fully grown would be overstocked but I don't plan on that happening because I will do the responsible thing and find good homes for the fish that I have if they get too big. So far my 225 is a better place for x2 footlong albino pacú than the LFS. I have 3' of width for them.
People who keep large growing fish in small tanks and damage their health are cruel but those are very different people to those that are growing out a fish.