Individual Details

It's hard to be sure given the common name, but in 1930 Robert was not in his mother's household. I found in University Park, Dallas Co, TX, the following single man listed as a Lodger.
Robert E. Thomas, age 22, b. TX, working as a traveling salesman for a shoe company.

1940 Census. Election Dist 13, Montgomery Co, MD, Hh 279
15141 N. Falkland
Robert Thomas, 32, b. TX - in Sulphur Springs, Hopkins, TX in 1935, special agent, government
Hazel, wife, 29, b. OK - in Houston, Harris, TX in 1935
Caroline, dau, age 1, b. D.C.

Wife was Hazel Taylor.

FindAGrave.com
Robert E. "Bob" Thomas
Birth: Nov. 22, 1907
Death: Dec. 18, 2000
Inscription:
B: Sulphur Springs, Tx. D: Dallas,Tx. Buried: 12/23/00
Note: Survived by wife Hazel Thomas who he married in 1936.
Burial:
Sulphur Springs City Cemetery
Sulphur Springs
Hopkins County, TX

The SSDI gives the last residence as Dallas.

Birth	22 Nov 1907	Texas
Marriage	15 Aug 1936	Harris County, Texas - Hazel Nevada Taylor
Death	18 Dec 2000	Collin County, Texas

Spouse

Hazel Nevada Taylor (1910 - 2002)

Father	Hubbard Harrison Thomas (1878 - 1918)
Mother	Virginia Clara Russell (1881 - 1976)
Sibling	Marvin Russell Thomas (1900 - 1968)
Sibling	Harold Hubbard Thomas (1905 - 1986)
Sibling	Virginia Thomas (1915 - 2011)
Sibling	Earl Franklin Thomas (1918 - 1996)