The optics were very bad. Diet soda is even worse than the real thing. If someone, for whatever reason, must drink cola, Mexican coke is the best. (There is a bad joke there somewhere) Mexican coke is made with pure cane sugar. It still has all of the artificial coloring but cane sugar, in moderation, isn't bad for most people. I'd opt for Sprite if I had to drink soda. All the same, it was stupid on his part be in that photo, whether he actually consumed the meal or not.
When I was a child, my mom and aunt took me and my cousin on a road trip. My mom's car ran out of window washing fluid and there were bugs stuck all over the windshield. They pulled over and my aunt poured a coke on the windshield and it ate the bugs off. Scary. So, yes, it doesn't surprise me about battery acid.
Many moons ago when I drank diet coke, I noticed white circles under my eyes if I had more than one or two. So, before people started talking about it being unhealthy, I quit. Once in a while, I'd have one if out to eat. Then, one day, when it had been a couple months since I had one, the server brought it to the table and it tasted like chemicals. It was repulsive. Most people who drink this garbage would probably have the same reaction if they took a couple of months off and tried it again.