It is a misconception that Rockne Tarkington is the only black actor to have a speaking role on The Andy Griffith Show. In "Howard's New Life (1967)," actors Sir Lancelot and Mark Brown, both of whom are black, have speaking roles.
It would seem unlikely that after four years of college, and ten years playing for the New York Giants, Flip would return to Mayberry to work with his father. But NFL players in the 60s only averaged $20-$25,000 a year. A retired player would not be set for life financially.
To get out of the piano situation, Arnold tells Andy that he's not very good at explaining things, and then makes his way quickly out the door. Two of Arnold's most defining characteristics are his tendency to shine adults, and the other is explaining everything to his friends.
Rockne Tarkington plays Flip Conroy. In 1974 he would star in "Black Samson," a fully R-rated exploitation film. It was about as far from Mayberry as you could possibly get.
With the exception of "Opie and Mike," Opie was always the smaller, less athletic kid, who was either prey, or dominated by older, taller boys. However, in this episode, when Opie's football team comes to his house to confront him, it's obvious that he is taller than all of them.