Do you think DEs just have a huge list of package names to app names, or how do you imagine this would work?
In reality, it's of course fully on Gnome, as it's part of their code. Nobody except for Gnome has anything to do with the name that's being shown.
The most recent HDMI versions are limited to 48Gbit/s, so you could fit almost 17s of a movie on a 100GB disk!