Einstein was being sarcastic when he said that, it was a dig at how arrogant and self assured Tesla was... But though Einstein did have a big effect on the modern world, Nikola Tesla really first invent and built almost everything that we define as modern. He even said we would have mobile phones...
What can I say. What if you were the most intelligent person on the planet? I know that the 'nerd' archetype, which often is just borderline personality disorder that I call 'cryptomania', but when you actually know how to talk about something that people can't follow, they often will be repelled and say you are arrogant.
I have had this problem all my life and I'm actually quite humble about almost anything else, and even my intelligence, it is certainly up there, but I will be the first to say that because of other things I don't put it to much useful application.
Well, I seem to be good at helping people learn things though... many times people have commented on posts that I consider to be amongst my better ones, that my way of explaining helped them understand something that nobody else had managed to convey to them before.