Why did my Macbook Pro shut down randomly?

This problem has been resolved, as I am currently using my Macbook Pro (mid 2012) to post this, but I am still very curious. I had my new iPad mini 3 plugged into my mac (most likely not a supported apple lightning cord) and was using my Macbook Pro to listen to some music on Youtube. I was navigating my iPad for some reason, can't really remember why, when I noticed that it wasn't charging. In the status bar were the words "not charging" which I thought was very odd. All of a sudden, my Macbook Pro just shuts off. Can't get any response from it, it had pretty much keeled over. I notice that the charger for my mac was a very dim green light, and the battery indicator lights wouldn't light up at all on the side of the Macbook Pro. I panicked, unplugged everything and tried rebooting it. Nothing. So I start browsing for solutions on my iPad mini 3, and come across one about unplugging the actual battery from the logic board. Long story short, that worked and now it's running again. Why would it do that? I'm thinking it could be the cord I was using for the iPad, but I've used that same exact cord for my iPhone 5S. I am clueless as to why.