The odds are overwhelming that the ball on the way down would nestle in the top of the tree and wouldn't be visible from beneath. The photos showed tons of balls in the trees. And in the rare case where a ball was essentially embedded in a way where you could see it from the bottom, the odds aren't great that it would show all of the markings necessary to ID it (Make, number, red dot, and line on the side and a custom hand drawn arrow on the side).
This whole argument is so similar to his embedded ball snafu. It came down to him verifying something that later turned out to be impossible and then him relying on the rules official for cover (who relied on his honesty to come to their conclusion). That loophole has always been there, but very few have chosen to exploit it throughout the last hundred years.
The vast majority of tournament golfers, and even club golfers have had to self identify rules violations that occurred when nobody else could have known about them. I would bet that everyone on this forum who plays competitively at all has done it multiple times (played wrong ball, ball moved at address, signed for incorrect score, extra wedge in the bag, violated one ball rule, etc). Has PR ever called a penalty on himself where the incident had no witnesses?