I repair medical equipment. I once took apart a device and found a safety circuit bypassed with an alligator clip. Not sure if it was forgotten or there to make something work as a repair. Point is, people do dumb crap.

I don’t get how just a simple credit button attached the grounding braid can somehow make the machine score points like crazy? Very weird and seems pointless... or pointful?

One of the craziest hacks I have seen was done by a guy who according to his daughter repaired pinball machines as a part time business before he passed away. He couldn't get a machine to start a game after coining it up so he drilled a hole in the side of the cabinet and had a string attached to a relay. She proudly showed me this machine that her dad fixed up for her a few years earlier. She said "all you have to do to start the game is pull the string hanging out of the side of the cabinet"!

I am just glad I was not one of his customers!

We tend to carry an electrical charge on us that’s different from the ground potential on the machine. Sometimes it’s enough to affect electronics. I’ve seen when debugging stuff that if I’m touching the metal rails or front panel it can trigger stuff . Depending on what part of the credit button it was touching and if it was also touching the face place you may have been sending enough random noise into the ground signal and that lets one of the transistors fire.