A preliminary injunction requires the fulfillment of 4 requirements: 1) the plaintiff will likely succeed in proving infringement, 2) the plaintiff will likely suffer irreparable harm without an injunction, 3) "the balance of equities tips in his favor", and 4) an injunction is in the public interest.
The point on which the injunction was overturned was 2); The court found that there was no causal connection between the alleged infringement and alleged harm.
In this case, Apple was seeking an injunction based on alleged infringement of a "unified search" patent, in other words, the technology that supports Siri.
