There isn't a single mention of Jesus Christ in that whole passage. This may come as a shock to you Christians...but not everyone who believes in God is a Christian.
However, Washington regularly attended Christian church services. His granddaughter (who was very close to him) wrote that she had no doubt he was a Christian.
To my knowledge, he never said anything that led to any thought that he questioned the devinity of Jesus (as both Jefferson and Franklin clearly did).
So it seems reasonable to accept that he was a Christian.
In his Proclamation (post #57) he refers specifically to both "Almighty God" and the "Lord and Ruler of nations." Only Christians understand the triune nature of God, and refer to both our "Lord" and our "God" interchangeably.
This may come as a shock to you Christians...but not everyone who believes in God is a Christian.
Actually, you might be surprised at how little shocks me any longer. Or any of "us Christians," for that matter. I am aware of deists and Bhuddists and Krishnas and Catholics and Wiccans, Muslims and Taoists and atheists. None of them surprise me, nor do I mistake them for Christians.