I think there is a good chance that the grounding post was soldered, and that it was a "cold" solder joint. I don't see any evidence of the solder wetting on the pulled-off ground post, which there should be if this was a good solder joint. A better focus picture would be good, but based on what I can see, I'd call it a manufacturing defect.Can't rely on a hinge to sink enough current to trip a breaker - that's why there's a safety ground wire to begin with.
Is the "splash" in that image indicating the original post was soldered? If so it should be rather easy to reflow the solder with the original post. Otherwise a strategically placed screw and a star washer under a binding nut should work...
Cheers!