I wasn't part of the earlier discussion but this is a courtesy lookup. Indeed there is kinship. Your grandfather appears to have been the youngest sibling born to Frances Marion Miller (26 Jul 1852 - 17 Sep 1934) and Missouri Hasseltine (nee: Guthrie) Miller (20 Aug 1852 - 6 Feb 1940). Both have find-a-grave memorials in Erath plus online death certificates https://familysearch.org/
Death certificates on parents has "good" info regarding their birthplaces. In addition to your grandfather and John Rufus Miller: James F. Miller (14 Apr 1879 - 30 Dec 1902), George Brady Miller (21 Jul 1881 - 3 Jun 1959), and Ellie Bird (16 Apr 1886 - 27 Nov 1918). I'm not related or acquainted.