It's a cool-looking fish but I'm not familiar with it. It looks like it's in a tank with Cardinal Tetras and Glass Bloodfin Tetras (both of which are wonderful species), but that doesn't mean that it's from South America. Looking at pictures on line, I think you're absolutely right about this being Petruichthys brevis, and it's one of the more colorfully patterned individuals. It looks like this species is from southern Asia, so the tank has a mixed geography.
