1) ah yes, 5kg if gold in this guy's neck has to be real!
2) a non-magnetic metallic mass that large will still likely screw up the image, if not the machine.
I seems like an easy mistake to make. The imaging was done, per the article "His wife told local media she had called him into the MRI room after her scan" and so the technician could have looked at it being gold colored and didn't apply critical thinking to presume it wasn't real. There was no concern about screwing up the image.
5kg gold makes a surprisingly slender chain, actually. I've heard 1kg gold is as big as an iphone.