Biden did commute the sentence of several other non-violent cases just last week or thereabouts, and Trump has been talking about Ulbricht for quite some time so it's not a complete surprise.
I guess the whole "murder for hire" thing excluded him from the "non-violent" category. But how that got tacked on seems very odd; the judge basically said "we didn't really handle it in the court case and it wasn't a charge, but it was mentioned a few times and it seemed basically true, so I included it in the sentencing". Like, ehh, okay?
To be honest, I don't really understand much of the logic ("logic") of the US justice system....