You went into a dorm room where an intoxicated co-worker lay on her bed, unbuttoned her blouse, and fondled and kissed her breasts. You don't have a criminal record. The district court thought your offense was only worth probation. It didn't even think you should register as a sex offender, so it didn't order it.
Too bad. Congress says you have to register. It's mandatory. Not a tough case. Doesn't even need oral argument.