That's correct. His parents are still not known. He is thought to be brother of Henry of Sudsbury. There are a series of great articles about him in The American Genealogies: 10:133-39, 11: 14-21, 15:227, 26:10-11, 61 :161-66, 63: 129-37, 65:241-47. and also in The Genealogist 6:131-41. There are some good older quality books regarding him:
Mary Audentia Smith Anderson, Ancestry and Posterity of Joseph Smith and Emma Hale (Independence, Missouri, 1929) 135-7
Mary Lovering Holman (and Winifred Lovering Holman),Ancestry of Colonel John Harrington Stevens and his wife Frances Helen Miller , 2 volumes (n.p. 1948, 1951)
Ray Lowther Ellis, A Genealogical Register of Edmund Rice Descendants (Rutland, Vermont, 1970)]
And just over the last few years NEHGS published some works that covered his descendants in "New England Ancestors" 3:4:50-51, 6:4:48-50, 9:4:48-50;