Is the triplet stroke something like playing the bones(not sure if you've played those)? Just loosening up your wrist and letting it happen...not trying to do too much
It is, but like the bones, you have to develop some control once you've achieved the "just let it happen" phase. If you didn't do this ... the entire technique for the instrument would just be happenstance and/or chance.
Playing a roll on a drum could be thought of as "just letting it happen" ... at first ... getting out of the way to the point that you let the drumsticks bounce freely. But once you learn to allow what the apparatus wants to do naturally, you've got to begin developing control and harnessing the natural rebound, etc. Learn to work with it ... then develop it further to the point that you have complete control of what you are doing/playing.