Not to be argumentative, but Forrest never referred to these men as "soldiers", he called them "Confederates". Wasn't all of the citizenry in the Confederacy referred to as Confederates? Could the general just be saying that these men conducted themselves as all other citizens of the Confederacy, not as slaves? I do not draw the automatic conclusion, nor am I aware of accounts of these men "fighting" or in the ranks of the soldiery.
I've seen this reference on many occasions as testimony by General Forrest of an organized group of Black Confederates. I do not believe one can automatically draw that conclusion from this statement.