Huh. Weird, I redownloaded it, and it was still 0.8.3 both in "Get Info" and in the app. Then I deleted all traces of Pixelorama from my Downloads and Application folders, redownloaded it again, and there was 0.9!
I'm guessing it was either launching the old app when I tried to open the new one, or the old .dmg was being opened after the download. Sorry for the confusion.