While he certainly was a Knight, he was not a Baron, the title "Lord of Horton, of Heton" refers to his manor:
↑ Cokayne, George Edward and H.A. Doubleday et. al eds. Complete Peerage of England, Scotland, Ireland, Great Britain and the United Kingdom, Vol. VI: Gordon to Hurstpierpoint, 2nd edition. (London, 1926). Online at FamilySearch.org, page 136: Grey of Powis, footnotes
Royal Ancestry by D. Richardson, Vol. III, p. 106-107
Archer, T.A. (1890). "Gray, Thomas (d.1369?)." Dictionary of National Biography, (Vol. 23). Wikisource.