There seems to be a confusion in Houston, 1882:8.

He quotes a letter supposedly from a "Samuel Houston", dated May 3rd, 1820.

My mother (her maiden name was Todd) died in seventeen hundred and fninety-five (1795), and was buried near Maryville, Blount County. My father died in kentucky, and was buried in a churchyard near Whipperwill Creek, Logan County.
Signed Samuel houston., May 3, 1820
Some facts which Gen. Sam. Houston Collected...have thrown interesting light on the history of the Houstons of Scotland...

This sounds as though the letter being quoted came from General Sam Houston, but elsewhere Houston, 1882 identifies his parents as Robert Houston and Elizabeth Paxton. The Samuel Houston whose mother was Sarah Todd was the son of John Houston (1726-1798). It may be that Houston, 1882 has mixed information about two families.