So I just hopped on MorphMarket to try and look at some arroyo stuff to help you out, as well as on WOBP. Funnily enough his old ad on MM for your little guy is still up, with him listed as on hold, apparently MM ads are slow to update. Lol
Anyway, since arroyo is normally more of a darker morph, like mahogany or chocolate, I'd expect it to darken the animal up instead of lighten it. But it also adds more distortion in the pattern, so since his pattern is busier it could be because of the arroyo. For reference, the only one it the clutch that I'm almost positive contains arroyo is the darkest hatchling in the center bottom, and the one to it's left may be a pastel arroyo, but mixing arroyo and leopard really makes ID difficult.
My best guess would be that his brother is either firefly leopard and he's the only superfly leopard, (which may not likely/possible due to the pairing) or that his brother is the one with the arroyo gene.
But the only way to know for sure is breeding him out. I'd breed him to a normal female, since he's superfly you'll minimum get a pastel arroyo. Then, if you wanted to, breed the pastel arroyo back to a normal to isolate the arroyo gene.
If you didn't get him for breeding purposes then I wouldn't worry too much about it, he's absolutely stunning and that's all that matters.