Thanks for the link. After reading it, and checking out the Eighth Amendment, I can understand why the district court felt that the longer sentences could/would be in violation of that Amendment.
We all complain about judicial activism, whether it's by the Supreme Court of an Appeals Court. What happened here is no different. The law mandates a minimum sentence. The Supreme Court has upheld minimum sentences. For the district court to decide that they weren't bound by the law is judicial activism, no more and no less. It's their job to uphold the law, not make it.