What Amon saw through her window excited him, he couldn't help but put up a little play for his viewer.
What Amon saw through Shiana's massive bedroom window is a man using a telescope to spy into Shiana's room and this man is none other than the fat guy that Amon and Shiana met outside her house, the same man who simps for Shiana and doesn't get anything in return.
Amon expected this from a man like him, spying on a hot woman from the comfort of his own home, a classy move, no one gets hurt and the one who is getting spied on doesn't know that they are being spied on.
The reason Amon is able to see the fat man is that he is not human, even though the fat man's room is completely dark, Amon could still see the man sitting on a chair with his eyes on the other end of the telescope, he is also shirtless and Amon's eyes felt assaulted by seeing the hairy obese man.
He had to look at Shiana's ass to get rid of that picture.