So many myths, actually, the name Buchanan comes from many lands. Remember the story that the scotch/Irish are not native to Scotland or Ireland but from the sea people who settled in the Spanish french border mountains. Who were from the sea people who raided Egypt in the early days. If you follow the genes, that's dang close.
But, there are outliers, there are Turkish, German and viking recorded words that sound the same, or ouuld phonetically sound like Buchanan, such as son of, buch. Depending on the type of boch, buch, Bach, it could mean cannon loader, to the book holder for the priest.
But, everyone says a Germanic name in Scotland identifies the family. No, just be proud, there is a history, that can be traced, good and bad, everyone wants to read of the hero's, but remember that for every baron, there is a horsetheif.