Is reddit.com mobile optimized?

There's a bug where opening a post from a subreddit's main page always results in a weird border, like it's opening the post as a floating dialog.

(Just to confirm tried it logged and out, same result: https://imgur.com/a/6yK9D8V)

That results in comments being squished down to a few characters wide and many many lines long

I used to think it was a "me" bug, but it's followed me across 4 iPhones over the years!

How can they have such an experience breaking bug on one of the most homogeneous major platforms out there? iOS only has one browser engine!