It is difficult to determine whether a child is having a behavioral tantrum or a sensory meltdown.  This article from offers a good explanation and some strategies for coping with both.  Ultimately, if as a parent or caregiver,  you are having a difficult time sorting or discerning the difference between behavior and sensory overload, a Sensory Assessment by a Pediatric Occupational Therapist can be helpful.  Here is the link:

Lizette Alexander OT Reg. (Ont)