Yes, I had noticed that discrepancy. It is not the first mistake I have seen in these notes. My guess is that this note was written with input from my G-Grandfather, who would have known his grandfather Samuel James Smith (Elder John's Son).
What is interesting is that if the geographic location is correct, then whoever passed this information down (Samuel James?), knew enough about where Isaac came from to know that it was now in a different county (or he only knew the current name of the area), which could indicate that some other family members of Isaac/John were still in that area when Smyth county formed - but that is pure speculation on my part.
Smyth/Washington county is pretty close to Tennessee, I could see some confusion, but it is good to see some agreement between this note and other records.
One note is that there are records of Sproles in Washington County - so that may be a place to look for records for the elusive Elizabeth, wife of Isaac.