Nick Fury could sense that Thanos was not bluffing. He truly knew.
The problem was, everything about him clearly marked him as an alien, from his strength and appearance to his technology.
But how exactly had he learned about this? Could it be... he had spies on Earth?!
Thanos's voice interrupted Nick Fury's wild speculation:
"You're overthinking it. I'm not bored enough to send advance scouts to a backwater planet like Earth. This is the power of technology."
Just explain, then. Why do you have to put Earth down... Nick Fury thought.
But soon, his attention was drawn to the technology Thanos had mentioned.
"Hey, did I hear that right? Technology? Someone like you believes in technology too?"
Tony's tone was somewhat mocking, a response to the other's disparagement of Earth.
But honestly, Thanos really did not look like someone who had anything to do with technology.
Pretty much anyone who saw Thanos would have the same first impression: Whoa, what a powerhouse. He's definitely a born warrior!
"Don't be so arrogant, Earthling!" Thanos looked at Tony and said earnestly, "Knowledge is the source of all power. Technology is also a form of knowledge, so why would you think I'd reject it?"
At this point, Thanos truly did not know who Tony was.
In the original timeline, the alien invasion and his sense that he and the others were too weak-and, most importantly, that blow from Scarlet Witch that showed him a future of utter despair-would ultimately lead Tony to abandon improving his own strength and seek outside power instead.
In the end, Ultron was born.
It was also this incident that brought Tony to Thanos's attention.
Only then did he discover someone so much like himself.
His ideal was to protect his world-the universe-but everyone considered him a madman.