I made myself curious, so I consulted Mister Owl.
Powell's birth name was John Wesley Powell and he was given the nickname “Boog” by his father as a kid who had a knack for getting into trouble. Powell played 17 years in the big leagues, 14 of which came with the Orioles. He hit 339 career home runs and won a pair of World Series (1966, 1970).
Garohntee Daddy didn't call him 'Boog' cause he was 'a kid who had a knack for getting in trouble'.
If you were a big, hulking homerun hitter, would you tell the fellas the real story?
No. Let's just go with the 'knack for trouble' thing.
Sidenote: He was one of my best baseball cards, till my mama (who I really love, I swear) threw him out.
p.s. What's 'Boog' got to do with getting in trouble?