Philip has since tweeted:
Confirmed. My bloody shutter was on too high on af101. Retesting now low lightHe's redone the test, and will probably post the corrected results shortly.
af101 still not as good. but its better!
Vimeo: Low light test: FS100 F3 5DmkII
UPDATE 9:00PM EDT: The corrected video is up. according to Philip the incorrect shutter "cost a stop." Vimeo: Low light test: FS100 F3 5DmkII