ReDigi on Secondary Liability

I was intrigued by the comment in the recent ReDigi holding to the effect that there were three distinct secondary liability claims in the case:  (a) contributory infringement; (b) inducement of infringement; and, (c) vicarious infringement (pp 14-15 of the opinion).  The judge finds that contributory infringement and vicarious infringement are established, so expressly does not rule on the inducement claim.  I can understand that inducement may be problematic if ReDigi was in fact advertising that it was a “legal” service, even if ReDigi was incorrect in the court’s opinion. But I also thought that inducement was generally regarded as a part, or subset, of the contributory infringement claim, rather than as a distinct third test for secondary liability.

In Perfect 10 v Google, the court seems to divide contributory infringement into two sub-categories:  Sony-style arguments relating to articles not capable of substantial or commercially significant non-infringing uses, and Grokster/Napster-style arguments related to intentionally inducing or encouraging direct infringement.  This second class seems to break down into the “inducement” and the “active participation with knowledge” sub-categories.  Is ReDigi doing something different in describing “inducement” as a third distinct form of secondary liability outside contributory liability, or is it the same thing, but phrased differently?