I agree with you. What else could it be?
What else? Arkancide comes to mind.
It is very likely not suicide. It is much more likely:
1) GLOC with the P-51 pilot
2) Loss of situational awareness by the P-51 pilot losing visual on the B-17 during the pursuit curve.
3) A medical emergency with the P-51 pilot rendering him unable to control the plane.
In any case it is a tragedy on the personal level for families of all involved and the loss of a national treasure. We have lost two B-17s in recent years. Not that many flyables left.
Unless you are familiar with airshows your opinion is totally out of line.