A little time will tell if he is a convict x nicar, or a really colorful CONVICT.
And the nicar being a male makes perfect sense. Convicts are a "nest fish" while nicaraguense are more like Africans (Loosely saying) the male nicar is not usually "there" at the nest, but patrolling the general territory while the female does her thing. So, it makes sense that you didn't see any nesting activity - although I'm surprised you didn't see any nesting on the female's part.