Both parts are machined forgings (not castings).
In the first picture:
The part on the left (in the mans right hand) failed due to fatigue. The beach marks on the fracture face are clearly visible in the photo.
The part on the right (in his left hand) shows evidence of fast fracture. Which would suggest it was over loaded when it had to take the load of the fatigued fitting. However, because there is not a real clear picture of the facture face, fatigue can not be ruled out.