Probably because George Washington was the first president of the US whereas Hanson was the first president of the continental congress.
Let's just say US historians go back and forth.
Under the Articles of Confederation, fully ratified in 1781, there was no separate President of the United States or executive branch of government. Instead there was a President of the Congress who had extremely limited powers, but was as much of a chief executive as the U.S. had. That was the state of things until the Constitution was ratified in 1787 and the election of G.W. in 1788. He took office in 1789. Until then, the President of the Congress was the President, as much as we had one at all.
One of the provisions of the Articles of Confederation was that if the Province of Quebec (i.e., Canada) wanted to join the United States, it would be accepted.
Legend has it that this is the origin of the Canadian reputation for politeness, for they were most gracious in declining our invitation to leave the richest and most powerful empire in the history of the world and join our broke-*** nation of farmers, and waited until all the Yanks were out of the room before bursting into hysterical laughter.