Sounds like you might have found one of the "good" Petcos where they actually take care of their animals and customers. Most of us have had iffy to downright bad experiences with our Petcos.
I think because they have to be kept alone, the males tend to bond with their human owners more than the females. Both my males are very social and like to watch what I'm doing - my guy Sherman even likes to swim around my fingers. Ahto is bonding with you, which is great because he realizes he's found himself a good, responsible owner. And I think he realizes you're the one who got him out of that filthy water and into a nice clean home.