Pull chances can't be accurate

I just pulled Osiren 4 times out of 5 legendary summon crystals.

During a 15x that he isn't a part of.

Can someone much smarter than me run the probabilities on that based on the epic draw pool? Considering the pool he draws from has an 86% without the 15x factored in and without pity factored in, and his pool contains 50 possible heroes. To draw the same hero 4 times out of 5 with those possibilities is probably like 1 in a billion or something stupid like that.

I know most of us probably already know this, but these pulls are absolutely not random or odds based.