He wasn't even tried for those charges, which should give us pause.
I'm surprised a judge is even allowed to site "unambiguous evidence" for charges that weren't even brought before the court.
I feel like judicial discretion in sentencing is pretty well understood, but I guess it could seem strange if you haven't spent much time reading about or experiencing the legal system.
Sentencing is a range. Based on the facts presented to the judge during trial and through third parties in the sentencing phase (victim statements, letters from your pastor, parents, friends, and teachers, etc.) judges can choose the low end of the range or the high end of the range. It's no more strange to give someone the high end due to unproven statements of assholerly, than sentencing being more lenient for good qualities that have never been proven.