Well, they did mean it for real. They didn't directly give me feedback on how to improve it, other than "go home, man". It's a personal choice in the end :)
For a defined 3-month internship where your primary goal is to suck up as much experience as possible at a young age during said internship, I think you can give insane work hours a pass and just accept that they're making the most of the short-term opportunity. Just don't let it become habit in a fulltime job and you'll be sweet.
Even for a 3 month period, I think 16 hours is overkill. I would say 12 hours is the upper limit. This is just my opinion of course.
In any case, good on Google for warning people about that, especially younger interns/employees. Some people just get into the lifestyle and end up realizing what they lost way too late. Work isn't everything. It's important to wind down by doing things other than what you do at work/school, such as exercise, meditation, or a just developing a hobby in general.
