A weapon can be triggered without it being intentional, see the goldsboro incident. The bomb went through three of four arming sequences as the plane carrying it broke apart, it's considered luck the fourth and a subsequent detonation did not occur.

> “Until my death I will never forget hearing my sergeant say, 'Lieutenant, we found the arm/safe switch.' And I said, 'Great.' He said, 'Not great. It’s on arm.'” https://en.wikipedia.org/wiki/1961_Goldsboro_B-52_crash#Bomb...

Also what you are describing is "One Point Safety" in which an external explosion or fire can cause a nuclear detonation. This is mostly true for the current US arsenal, but wasn't in the past. It's one of the main reasons why the Little Boy design was so poor for safety, it only required one (preferably intentional) explosion