This is about remote mounts which should be present or, let’s say, available all the time. These should be mounted to /mnt/. Removable drives like a USB drive are and should be automounted to /media/.
Why would you want to mount a USB drive manually to /mnt/ via fstab? I’d guess that fstab mounted removable drives wouldn’t show up as safely removable. But it’s just a guess, somebody more experienced has to comment on this.