It says the 6.7m figure for Switch includes the digital sales, so maybe 6m is physical and it sold 0.7m in digital? Seems awfully small though.
6mil is sold with digital. 700k on store shelves. Add wiiu is 1.5mil. that not low considering install base and BotW is almost the best selling Zelda in less than a year with the best legs of any Zelda thusnfar!