Can you either provide a picture or the make/model number of the device?
It could still be a USB stick or a drive in an enclosure and that drive could be a SSD or HDD.
But in general, being external, they are more prone to failure simply due to being exposed to drops, knocks, and improper disconnects.
If it's a HDD, they hate any bump, especially when connected and rotating.
IF SSD, they also fail, especially the low end, cheap units.
Take the failed unit to another PC and connect it, if that PC also fails to see it, chances are excellent the drive has failed. In some cases, it could also be the external case it is in, so removing it from the case and connecting internally into a desktop PC via the data and power cables would test that theory.
In short, drives, of all types, fail - that's why we backup!