Jamie Dimon is a very smart man. He has to be. And smart men know the consequences of their actions and the influence that his words have on markets around the world. He had to know that his negativity on Bitcoin would lead to a price drop. And if he didn't view Bitcoin as a threat, why bother commenting on it, especially with such bitterness that he would fire any banker supporting the coin. He knew what he was doing, and he knew that he was going to make a profit on the dump.
Short version = Who knows?
Longer version =
I agree that Jamie is a smart man, he would not be where he is today without lots of smarts, however, he has spent a lifetime essentially working one system. He has seen many bubbles come and go and has probably created and profited from most of them. He might be looking at Crypto as being a drop in the ocean when compared to traditional currencies - and thus dismissive of them - note he was not dismissive of blockchain generally.
He might well believe that HIS world will not change significantly and his position in it will never be challenged by what he sees as an upstart currency/bubble like BTC.
Who knows?