Strumming won't help in this situation. What really happened was that the second yellow was already inside of the hit window, and he tapped red before releasing yellow. And for whatever reason, the game thought he tapped yellow again, because there was a change in his fretting, which in this case was hitting yellow while anchoring red. It makes absolutely no sense, I know. But he held yellow for too long by the time he tapped red, when he should've released yellow before tapping the red.
As someone who knows how the World Tour tap engine works, here's what I think what happened. The World Tour tap engine has an overlapping hit window. And this is especially crucial if there are several notes close enough together, the game checks for which color you have fretted, and it picks up that note even if there is another note before it. So what happened, after you hit that first yellow, the second yellow was already inside of the hit window. But instead of releasing yellow and hitting the red, what you instead did was fretting the red before releasing yellow, and the game picked it up as a change in the fretting (since notes can be anchored), causing you to hit the second yellow before even getting the chance to hit the red. It's absolutely busted and it sucks really hard. :(
oof next time my guy; Matt Way and I were talking earlier about how this is the first time 2a's been done in venues and is a seriously dope proof of concept moment in GH history lol