What is lapsang souchong? Why does it have such a smoky taste?

Sources:

• https://en.wikipedia.org/w/index.php?title=Lapsang_souchong&oldid=874580993
• https://sevencups.com/2013/11/the-demise-of-tongmu-lapsang-souchong-black-tea/
• https://www.therighttea.com/lapsang-souchong-tea.html
• “The Tea Drinker’s Handbook”, p. 159
• http://nicky_smith.tripod.com/neon.html
• “The Tea Enthusiast’s Handbook: A Guide to the World’s Best Teas” p. 133 (Loc. 2192)
• https://en.wikipedia.org/w/index.php?title=Russian_Caravan&oldid=872883877
• http://www.flavorandfortune.com/dataaccess/article.php?ID=617
• http://sensibiliteas.blogspot.com/2009/01/sherlock-holmes-and-his-cup-of-tea.html
• https://www.thekitchn.com/cooking-with-tea-smoky-lapsang-52170
• https://www.teaformeplease.com/blog//2017/08/the-real-lapsang-souchong-and-dangers.html
• http://theteastylist.com/2012/01/23/pillars-of-smoke-churchill-cigars-and-lapsang-souchong-tea/
• https://theteaspot.com/steep-it-loose/loose-black-tea/where-does-lapsang-souchong-tea-come-from/
• https://verdanttea.com/the-legend-of-lapsang-souchong/ (yet another origin myth: bandits burning down sheds)