The English were in the area before the letter .
“Allying themselves with the Mohegan and Narragansett, the colonists attacked a Pequot village on the Mystic River (near present-day New London) in May 1637. Encircling their foes under the cover of night, the colonists set the Indian dwellings ablaze, then shot the natives as they fled from their homes. “http://www.u-s-history.com/pages/h580.html
But if the letter is not even referring to the the sites at Gungywamp ,then that is even more problematic . “, 'at or neare Pequot' could have been referring to anywhere east of the Thames River, and from the sound; north to Lantern Hill and Long Pond. This area would represent where the Pequot settlement was, in the early 1600's (McBride, 1990). “