It looks like you are pretty closely related. There was almost certainly a non-paternity event in which the son did not use the surname of his biological father. I suspect that your ancestor may have changed his name for some reason. Brown is a good alias to escape attention.
If you will give me the surnames of the two matches and theirs and your kit numbers, I will take a look at the results (assuming all in the appropriate surname projects). Y-Search is down, so it cannot be used as a reference. Otherwise, you can cut and post your results here and post the differences. You do not need to post the marker names, except for the mismatches. Simply post them in FTDNA order.
I suggest all taking a high-resolution SNP test to make sure you are in the same haplogroup. I would use 23andMe, since you get a lot more for your money ($99). (They use a different nomenclature than FTDNA, but, if you post your results here, I will convert them.)
You may also find that you are related to them. It would be beyond good accuracy (up to 3rd cousins), but matching segments may still show up.
If he showed up in Central TN, it is very likely that he migrated from the Piedmont areas of North or South Carolina.