"You sure it's–" Kara or someone like her mumbles in Oliver's ear and he cuts her off, "Yeah, it's his kid."

So to put it simple, it's a crossover and they are Kara and Oliver you know but they aren't the people you know. They are...Nazis while you are Flash's kid.

Why did they kidnap you from star labs? Probably has something to do with multi-verse or you at least hope.