Harry was looking at the black-haired boy with envy. He can always see through Solis" charades and he hates how the boy can manipulate others. The Dursleys, classmates, even the mailman. Solis is that A+ student who's respectful, that parents and teachers use as an example and it makes Harry mad that no one can see Solis uses that leverage to get his way. That the picture perfect child is just want he wants others to see.