It's true that pedophilia is not synonymous with homosexuality; different pedophiles victimize different sets of youngsters ~ same sex, opposite sex, or both.

The actual reason why paedophilia is not synonymous with homosexuality is because paedophilia is an act of criminal sexual abuse committed upon a minor, whereas homosexuality is normal sexual behaviour between consenting adults. The gender of the minor upon whose person the acts are being committed is as irrelevant as the gender of the person committing them.