What is the chance of this to happen!

So i was playing mage reroll trying to get vex 3 star. I already have 5 nami, and then in the 4-6 pve round i got a gold orb that give me 4 nami copy! which make my nami instantly 3 star! Then i start to losing against a varus 3 in late game. But then i hit this charm! This is my first time ever getting a 3 star 5 cost this way. Such an insane game!