Length contraction and time dilation in relativity

[Kennedy]

Alternatively, imagine that the rod is at rest in the particle rest frame and that in the lab frame the other end of the rod passes the position where the particle eventually will decay at the same time as the particle is created. Since the rod is length contracted, it will indeed be longer in the particle's rest frame. However, in the particle's rest frame, the particle creation is not simultaneous to the event that the other end of the rod passes the position in the lab frame where the particle will eventually decay. Therefore the length of the rod divided by the velocity of the lab frame will not give the correct time.I am going to stop you right there because this is a fundamental misunderstanding of relativity. There is no way you can identify a particular frame as a "moving" frame. All movement is relative, in classical mechanics as well as in special relativity. Relative to the lab frame, the particle is moving. Relative to the particle's rest frame, the lab is moving.

I'm very very very confused, but yes I understand that all movement is relative. That was a poor choice of words on my part.