The song the the Jocks 🏴󠁧󠁢󠁳󠁣󠁴󠁿 are singing is called "The Bonnie Banks o' Loch Lomond" - it’s is a Scottish folk song rooted in the tragic aftermath of the 1745 Jacobite Uprising, written from the perspective of a captured Scottish rebel facing execution in an English prison.

"You'll take the high road, and I'll take the low road" relies on an old Celtic myth that a Scot who dies in exile will have his soul transported ("low road") back to his homeland.

As a result, the executed soldier's spirit will return to the beautiful banks of Loch Lomond much before his released friend can walk home via the physical "high road."

Paul Robeson version:

https://youtube.com/watch?v=feLT7Btuqpc