For an aeroplane component to fail from fatigue, seems to indicate, that at least some calculations were faulty.
It is possible, however, that manufacturing problems in the forging or machining, did lead to the failure.
We rely on good, skilled people to do the necessary engineering detective work, as to just exactly how the failure happened, and what needs to be done, to ensure it doesn't happen again, within regular use limits.
Or possibly, the loads encountered were greater than those the calculations suggested would be met.
'Detective work' should start with an open mind, not vague suggestions that engineers have cheated in their exams.
I've still seen sod-all in this thread about the immediate circumstances of his failure, or indeed about it's potential consequences. All we seem to know is that something big and photogenic broke - twice...