One concept that I find frustrating is the misconception that some people have about knowlege. Some time you should take a psychology class and study knolege and perception. The human eye/brain can do things to people especially in stressful situations, shooting a big game animal is a fun stressor but no different than any other stressor. Most guys that shoot a big game animal that isnt legal "know" that the animal is legal and it turns that they are wrong. It can happen to absoutely anyone because your brain can trick you. Have you ever seen the paragraph written with no vowels that floats around, less than half the population realizes the vowels are missing.
He could have seen than animal at 100 yards with 24 power binos and still convinced himself it was a true spike. Because he seems to be a stand up guy I almost garentee he will pass on animals in the future that are legal because this experience will change his perception of future situations.