I had wondered if he was the older brother of John Carson Lewis who was killed near Denmark, TN and a grandson of Seth Lewis I of Opelousas.
The confusing issue is the older brother's name seems to have been Seth William(s) Lewis, possibly called Will, born abt 1829.
(But the Confederate records show that he was born in Georgia, which does not quite fit).
He had enlisted for the Mexican War but it does not look like he ever got to Mexico. In any case, the Lewis I am working on died in NOLA in 1870, possibly of smallpox.
So, bottom line, they may be two totally different people.