That looks like basically a cheap robe that is cut to look like a yukata. A yukata is kind of like a kimono but it is made of cotton and is thin and used in the summer. Much less formal than a kimono, and less expensive. But he's not wearing it like a yukata--it's not tied right, it's too small for him, and he just has a string to tie it at the waist, rather than having an obi. This might be supposed to be a humorous picture, or else it might be a quick tourist photo with little set up or preparation.