Your correction only compounds the confusion of the quotation, which refers to the diameter of Pluto, and the size of the earth.
The statement that Charon is 1/2 the diameter of Pluto is correct to reasonable accuracy, but its diameter ( as you state,) not its size, is concommittaly about 1/10 that of earth.
Gosh, I hope I got that right!
"I try to do things but they don't work out." - INSTITUTIONALIZED by SUICIDAL TENDENDIES
;’)