Is this supposed to happen in ranked?

So i was plat 5 2 days ago and went on the biggest tilt of my life and got demoted all the way down the gold 3 i finally got up to 81 lp from 0 in gold 3 and was duoing with my plat 3 friend when we won the game and i ended up in promos but had a win ( a checkmark in the slot for one of my promo games" how did it happen? does it have something to do with him being in his promos for something?