In part, Lindsay says:
"The big grey man is often said to be Scotland’s Bigfoot and the stories go back hundreds of years.In the 17th Century, a man of the clan Murray was reported as having captured a wild man in Craigiebarns Rocks and a chained wildman still appears in his family's heraldic shield. The next written report I could find was in 1791.
"Poet James Hogg, known as the `Ettrick Shepherd`, described seeing a huge figure on Ben Macdhui whilst tending his sheep. As he watched the halo, which had formed around him due to the combination of sunshine and the mist, he looked up and saw a huge, looming figure. He fled, not stopping until he reached some of his fellow shepherds. Hogg later said he believed that the phenomenon, which had so frightened him was, in fact, an uncommon natural phenomena known as the ‘Brocken Spectre’ and was a reflection of himself caused by the weather conditions - so could the grey man be just an effect of climatic conditions?"
And, here's the rest of Lindsay's illuminating post.