Hey huntersdad and thanks for the analysis. And I think you are right. But the problem with your analysis being right causes even more confusion to me. As you can see on the focus pictures the locking on focus point was directly on the bird. The 4 others are only helping AF points and they did not lock onto the bird. (Original from the canon AF Maual for the AF system of the 7D II: AF point expansion (Manual selection ) Focus using one manually selected point assisted by 4 other AF points (up, down, left, and right)).
If I put the center AF point on the subject ant the camera then focus on the background then I do have no control of the focusing. I basically can not rely on the information: this is the focus point this is where the subject will be in focus. Then it is more like a bet or a guess and I can hope but it is not something I can influence.
This is what the handbook has to say about a single focus point:
Single-point AF is a mode where one manually selected AF point is used to focus. For experienced photographers or when it is easy to track the subject with a single AF point, AI Servo AF can be utilized when continuously shooting moving subjects, however, this mode is more effective for shooting still life and landscapes with One-shot AF mode.
as ist says MORE for: shooting still life and landscapes or easy to track the subject
but birds are not so easy to track. Thats why I bought this camera because i has 65 AF points.
Should I have than better bought a camera with only 1 AF point???
You are absolutely correct, so let's analyze your picture.
Main point on the bird. That's good, but there wasn't enough to lock focus. So, the camera kicked in the surrounding assist point. The top assist point is clearly on the water. The bottom assist point, while it is on his legs, also picked up the water because there isn't enough contrast between the water and the legs. 2 points lock focus on the same area = where you're focus landed.
Tracking this bird vs. tracking a bird in flight are two different things. The manual, when it says "tracking", is talking about tracking something moving more rapidly. In your situation, the bird is barely moving so single point could have worked.
This camera takes some time to learn. It is different and has different requirements from any other body I've shot. You only learn it by doing things right and doing things wrong. More points isn't ALWAYS better, but provides better options than one point. Take your time, shoot, learn from your mistakes and you'll find yourself getting more confident each time out.
Here's one from this past weekend, 7d2/1.4x/600II: