That "footage has not been modified" statement is probably to get ahead of any speculation that it was "cleaned up" in post, after it turned out that the Sora demo of the balloon headed man had fairly extensive manual VFX applied afterwards to fix continuity errors and other artifacts.
The studio was pretty up front about it, they released a making-of video one day after debuting the short which made it clear they used VFX to fix Soras errors in post, but OpenAI neglected to mention that in their own copy so it flew under the radar for a while.
> While all the imagery was generated in SORA, the balloon still required a lot of post-work. In addition to isolating the balloon so it could be re-coloured, it would sometimes have a face on Sonny, as if his face was drawn on with a marker, and this would be removed in AfterEffects. similar other artifacts were often removed.
