To help determine if that is him, you need to trace back John T Garnett to his Virginia home and look for a John Bush in the area.
That really wouldn't prove anything, but it might help find the John Bush who was living with the Garnetts.
I didn't get far with that. Here are a few more listings for John T Garnett in the Baltimore City Directory:
1912
no Louis* or John T*
1913
Louis Garnett*, laborer, 117 N Vincent
no John T*
1914
John T Garnett* laborer, householder at 1018 Whatcoat
Louis Garnett*, laborer, 1018 Whatcoat
1915
John T Garnett* laborer, householder at 1700 Woodyear image 619
(despite what ancestry's links say, John T Garnett is not the same man as John E Garnett. John E was white:
1913 Baltimore City Directory
John E Garnett, laborer, 1343 Hull < no asterisk)
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so I looked for a John T Garnett with a brother Louis, but didn't find one.
There is a John T Garnett in Saluda, Middlesex County VA, in 1880, married to Sallie Anderson/Tobb or Carter.
And there is a William J Bush family in Saluda, born 3 March 1870 to Charles Bush and Hannah Foreman. William didn't marry until 16 Mar 1897, to Pelle Morris, and they had 2 young children on the 1900 census, neither named John or Dennis.
so, Saluda might be a place to look further, but I didn't find your John Bush there.
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And - do you know, or can you find out, if John had any brothers or sisters, when did he die, etc? Please post everything you know about the man, even if it is just a family story (if it is, say so). Anything might be helpful, you never know.