i was wondering if he thought it was an error
Was just joking dude. Don’t quite remember the Rebels sequence, but Obi-Wan does not record this message in EpIII (at least, not on screen).
it was the part in episode 3 where they use the thing in that room to warn any surviving jedi
Not sure: Obi-Wan just recalibrates the fake clone message so the surviving Jedi wouldn’t fall into the trap.
It’s unclear in Rebels when he recorded his message (https://www.youtube.com/watch?v=oaEG6c2LZic). So it might be a continuity issue between EpIII and Rebels, but I think he does record it later.