Registered sex offenders aren't necessarily pedophiles, are they?
Not all of them are. A sex offender is anyone who commits that type of a crime (a sex offense) while a pedophile from a legal standpoint in terms of sentencing is a sex offender who committed their crime against someone under a certain age (usually pre-puberty).
No, a pedophile is anyone who has sex with someone below the age of consent... in most states in America, the age of consent is somewhere between 16 and 18, though they might have close-in-age exemptions for people younger.
So, worst-case scenario, a "pedophile" could actually be an eighteen year-old who slept with a seventeen year-old and had a really harsh sentencing from the judge.