1. what is the horizontal movement being reported in CAESAR II hanger report?
If you assume "Y" is up, this is the movement of the hanger node in the horizontal (X, Z) plane.
2. is that the movement of the hanger from vertical position?
This is the movement (displacement) of the hanger node, it is not an angle.
3. how about the cans, can the spring move in horizontal direction in cans?
If you don't restrain the pipe in the horizontal plane, yes this movement can occur numerically.
4. if yes, what is the limit for that movement? 4 degrees?
CAESAR II imposes no limits on the solution. This is something you will have to check/verify.