It is my belief that any time you do something intended, it is skill. If you call the kick to the corner, and make it, even if you think you don't know where to hit the rail, and just wing it, it is skill. You may not even realize that you have enough skill to make it, but if it goes as intended, you have just shown that you do indeed have the skill to make it.
Now, you may not yet have enough skill to make it several times in a row, or even better than 50% of the time. But you do have enough skill to make it at least once, and that is all that is required.
That is what great shots are. Low percentage, but yet made. If you take the stance that the kick on the 8 was luck, then you also have to take the stance that there are no great shots, only all luck shots. Terrible attitude to take, and it only denigrates your opponent to make yourself feel better because you feel you couldn't make it on demand one time.
One only has to understand that there is a large difference in skill level from making it one time on demand, to making it every time, or most of the time on demand. If it was made, it was skill. Same as with any other shot.
One must also understand a difference here. If he calls the kick to the corner, and it goes as stated, as a one rail kick straight in to the corner, then it is skill. However, if he makes the same call, but his kick is a little long, and the 8 banks two rails into the intended pocket, then it is luck, not skill. It would be luck, because he missed what he was intending to do, even though the end result is what he wanted. The same can be said for any straight shot that hits the rail before it drops in. In my opinion, you actually missed the pocket, but got a little lucky because of the leeway of hitting the rail and still making it when hit at the right speed. The higher skilled person makes balls cleanly. The lesser skilled person utilizes the rails to help make balls.
So, is it skill or luck when hitting the rail when making an open shot to a pocket? Or is it a little of both? One had enough skill to at least get close enough on the shot to allow the rail aid to pocket the ball. But not enough skill to make the ball cleanly. So, if the ball hits the rail, did he slop it in, or use skill to make it? I say he used skill. While an adequate level of skill, not a very high level of skill.