no they are different. difraction is the splitting of light into its differnt components and reflection is throw back of light (its component remain same).
intensity falls since light is splits into its different components as a result its strength or intensity decreases.. ummm imagine a twig, when u break a single twig it is easy since strength of single twig is less however if you take severeal twigs and then try to break it then it would be a bit harder since the strength of individual twigs add together. to give a grater strength.
in terms of physics intensity is defined as power of light trasnfered per unit area. since light is splits into its components its power also splits; individual component of light move in different direction with thier invidual power. as a result as a whole the intensity of light decreses.