The mysterious Indian corkscrew

There's an interesting corkscrew that has come up for auction several times over the past year and a half. The corkscrew itself is a bone handled Henshall with a faceted shank and button, which in itself makes this an interesting and somewhat rare corkscrew, but the real oddity is the inscription. It's carved "Sir William Johnstown Indian Agent for Geo III N.Y. 1763 A.D." I bid on it the first two times it came up for auction, but it sold for way more than I was willing to pay. It first came up for auction in May 2021 in Maine, then again in November 2021 after the first sale presumably fell through. Then, a couple days ago it sold for $1,650 at an auction house in Florida. At these prices, the buyers are most likely not corkscrew collectors, but history buffs. The glaring red flag to me and my fellow corkscrew collectors is that the corkscrew is dated 1763 which is over 100 years before this corkscrew would have been produced. Who was Sir William Johnson and why would someone create what is most likely a fake corkscrew? A quick search resulted in a rather large Wikipedia page on the man:

"Sir William Johnson, 1st Baronet of New York (c. 1715 – 11 July 1774), was a British Army officer and colonial administrator from Ireland. As a young man, Johnson moved to the Province of New York to manage an estate purchased by his uncle, Royal Navy officer Peter Warren, which was located in territory of the Mohawk, one of the Six Nations of the Iroquois League, or Haudenosaunee. Johnson learned the Mohawk language and Iroquois customs, and was appointed the British agent to the Iroquois. Because of his success, he was appointed in 1756 as British Superintendent of Indian Affairs for all the northern colonies. Throughout his career as a British official among the Iroquois, Johnson combined personal business with official diplomacy, acquiring tens of thousands of acres of Native land and becoming very wealthy.
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Johnson commanded Iroquois and colonial militia forces against the French and their allies during the French and Indian War, the North American theater of the Seven Years' War (1754–1763) in Europe. His role in the British victory at the Battle of Lake George in 1755 earned him a baronetcy of New York. His capture of Fort Niagara from the French in 1759 brought him additional renown. Serving as the British Superintendent of Indian Affairs for the northern district from 1756 until his death in 1774, Johnson worked to keep American Indians attached to the British interest. Johnson's counterpart for the southern colonies was John Stuart."

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