Different question on a shot like this one... if the cue ball hits the rail and the ball at the exact same time. Is it a foul or is that a legal hit?
Great question. I'm going to take a stab at it but would love to hear what Bob Jewett or Dr. Dave have to say about it as well.
The real question here or at least the question that has to be answered first is how would you know if it the cue ball hit the rail and the object ball at the same time? Or how would you know if the cue ball hit the rail very slightly first but was still in contact with the rail when it then made contact with the object ball? The latter is rare but possible although the reverse (still being in contact with the object ball and then hitting the rail) not so much.
I think if it is your typical referee who is going by what they see/hear, then just like the answers you got in this thread and every other "was this hit good or not" thread like it, half the refs are going to call it good, and half are going to call it bad. When it is that close your typical ref is going to be wrong half the time if they are having to rely on being able to see it because it happens too quickly to be able to see it.
But if it is an exceptional ref like a Bob Jewett or a Dr. Dave, they know how to definitively determine what actually happened based on the ball reactions and don't have to rely solely on being able to see which impact occurred a thousandth of a second before the other one.
That being said, if the cue ball truly hits the object ball and cushion at the same time, more often than not it will react the same way it does when the cue ball hits the object ball slightly first and so a great ref like Bob or Dr. Dave is going to call it a good hit because the ball reactions are usually going to be indicative of a good hit. Who knows how the average ref is going to call it as they are going to be wrong half the time. Flip a coin. But to answer your question more directly I think hitting both at the same time is a "tie goes to the runner" type thing and is to be considered a good hit, and the rare exceptional ref will usually be able to tell it was a good hit based on the ball reactions but the typical ref is going to be guessing.
For the record I think there is a small possibility that this is in fact just one of those cases where the cue ball was in contact with the rail and the object ball at the same time. The frame that shows the cue ball in contact with the object ball is missing so we just don't know for sure but it was close.