Help understanding Victory Conditions
So I’m play with some friends and I’m 1 turn away from hitting 100 points in Science victory to start the 5 turn run off but it also just so happens to be the same turn we hit 60% in the modern age changing the victory difficulty to 1.5x which also puts my friend into the Cultural victory on the same turn as my Science victory but we find out that he only has to do 4 turns for his cultural victory while I have to do 5 turns for my science victory though we get them on the same turn.
I thought it was always 5 turns for a victory after you met the conditions. Why did he only have to do 4?
And if we both did win on the same turn how does the game decide who won?