Fantastic. I didn't watch the video (link?) so some of what I say here may have been covered.
This make sense because the ignition timing is identical. To be honest I would have expected a very slight difference in power, maybe 5-10hp, without knowing about the timing curve. But in all my time tuning cars on dynos, I've noticed a much bigger difference tuning ignition than anything else, even boost. This is usually because people turn up the boost first to feel a difference driving the car around without changing anything else, but it often nets little peak power increase - but does often give much more peak torque which makes the car feel much faster. Timing is where all the power is made. On my own personal car, I went from 27psi boost, 280whp, to 22psi boost, 365whp after jumping on the dyno to tune ignition. What a difference. Eliminating boost from the equation here, we're left with only fuel and ignition, and if ignition is the same... well, results speak for themselves.
Did they mention anything about knock or detonation? I'm assuming these engines have knock sensors and they didn't see anything? If they were able to keep the timing at 29 degrees over all fuel grades without knock, I see absolutely 0 reason to run higher octane in this application. Seems like they're not running into detonation issues, so the compression ratio could potentially be increased which would justify the use of higher octane fuels.