Can placing metal on a alternator cause something to mess up?

What is your question?

My car would not crank I was about to give it up but my brother said put metal on the starter but I accidently put metal on the alternator while my mom turned the key it got the car started but I heard putting metal on a alternator can cause it to fry things, is this true?. Also why did the car start with metal touching the alternator?