> Andrew Tanenbaum: I said that his work was amazing and thanked him. He shrugged me off. I think he felt busy or didn’t care. I was happy that he listened.

I have the same reaction to people thanking me out of nowhere especially when I am deep into my own thoughts and it's awkward to say something after the shrug. The realisation comes latter. So there is a chance he did appreciate your thank you but couldn't reply back properly.