IMHO, as you can see on the second image, the log is almost split. The knife just stuck on the bough knot. It looks small on the image, but it creates a curve in the wood structure which the knife's edge started to follow. The log parts are held together by another knot, which you can see on the second image. So, the back of the blade was still forced to stay vertical. (Well, I'm not sure if I'm explaining this clear enough? But that had happen to me zillions of times).

It's not that big a log for this knife. So if you feel it's too hard to split for its size - something is wrong. Just start at another angle, or better yet drive in a thick wood wedge instead, especially if the log has many knots.