If you are referring to the John Delafose tune, also covered by Cedric Watson and Corey Ledet, then your guitarist is mistaken. Using the G row, and pulling a flat note off of the C row, that song would be in D. The guitarist is hearing it in B minor, the relative minor of D major, because your last note is a fat B. Tell him to romp on a D chord, or even better, a D7th chord and go with it.

I wanted to also mention that it is very similar to what is being done in BooZoo's "I wanna go home."