Steve Rogers: You know, I really miss the days when the weirdest thing science ever created was me.
Ultron: [speaking to Quicksilver] You and I can hurt them, but you [turns to Scarlet Witch], you're going to tear them apart from the inside.
Ultron: I'm going to show you something beautiful...everyone screaming for mercy. You want to protect the world, but you don't want it to change. You're all puppets tangled in strings.
Answer: It's not an in-joke about real life. It's just a direct reference to Loki mind controlling him.
Greg Dwyer