I remember them specifically announcing that development had begun after the initial trailer reveal. Something along the lines of "Development for a Breath of the Wild Sequel has officially begun", so the two year marker isn't too far out there I'd think. They already had the world built, so...
Just a trailer with some flashy gameplay and scurried story bits, topped by a 2022 release window. Development really began two years ago, so I don't expect them to do much with it this year.