I saw "white slave" once and other terms very close to it when describing slaves that appeared caucasian in runaway slave notices. some people believed that the way to find a "white nigger" (which is what they were called by traders) was see whether they avert their eyes and stand aside for white people. anyone who did that, regardless of appearance, could be detained. if they could not provide proof that they were free, or prove they had permission from an owner to be where they were, they were sold at auction. there are actually a lot of court cases where people have filed for an injunction to prevent themselves being sold pending a court case to determine their slave status.
I cannot find him in any census, but the family I believe he's connected to is enumerated as white.
I've been searching court records. there aren't many online. I figured that if he was indeed sold to the May family as the account indicates, that there should be a court record. I may have to call the county courthouse this week to find out if they have the records... but, if the May family historical organization has them, or someone connected to them has them, I thought if they would share that would make this a whole lot easier!
I think another source might be newspapers. I've been checking all I can find, but haven't turned anything up yet there either.