He couldn't pull of the high notes on the chorus - You got proof of this because I've heard him hit just as high notes, try listening to Bicycle Race off the same album. That excuse kind of falls flat on its face.
He couldn't pull of the high notes on the chorus, so he went with the growling. It's so obvious, but hey, it's hard to cover Cornell. But it's kinda funny to hear the growl when you were expecting the high note. But I gotta say it's atrocious, it doesn't sound good. Although he did great with the verses, and the final line of the chorus "I trieeeed to liiive". Musically is practically the same, which is awesome.