what these numbers don't seem to keep into account it the increase in ticketprices... Also the production costs of the movies are again higher than in 2015. So comparing the years purely on boxoffice income is useless..
Well, if you have epilepsy and you know that even a simple video of strobing lights can induce it, than yes you should make sure autoplay is off. As there are many video's who have strobing effects and might be dangerous to you..
You should protect yourself, it's not the responsibility of someone else..
So if there is an option to block autoplay, then IMHO he himself is to blame, not the person who send him the video/animated gif..