I don't think he did anything wrong
Normal calibers when shot against steel exhaust most of their energy into the steel. The big 50 has SOOOO much more energy, that the steel can't absorb the greater part and you have a ricochet, in this case a bounce back. With almost any caliber against steel that is somewhat solidly mounted, you will find lead cores and jackets bounced back to some degree. Want to make things worse, try AP steel core bullets against thick steel. If it doesn't penetrate, it comes back at you as the steel core doesn't mushroom and transfer energy like a lead core.
I have shot the new fragmentation type pistol bullets at steel at 7 yards and you can occasionaly feel some of the core materials bounce back against your face and or hands. However, the material is pretty must dust at that point and can't (or at least I should say is designed not to) hurt you.