Suntan sauce bird

What could have caused this to happen to the heavy steel flatware in the restaurant I was in? - restaurant flatware

I was in a restaurant, a couple of years, and when I took the knife holder came with him! My cover has become highly magnetized. It took three or four pounds of pull them apart. If I leave the piece apart in five or six inches, such as jumping and restore. As far as I know, I was the only object is magnetized. What do you think could cause that?