I turned on personal hotspot for a few minutes on my iPhone and connected to it from my laptop via WiFi. Later I checked the usage and it accurately shows 9.9MB for my laptop. It it also shows 138MB for “other devices”. What does this mean? I did not connect any other devices. I’m on iOS 14.6.
I believe the "Other Devices" section is for devices that: A. Use little data, so they don't get their own section, but are instead combined with others. B. Do not have names that your device can identify C. Have names that are Private or actually called "Other Devices" (I doubt the latter would ever happen)
My guess is that it is either devices you have connected to before, or someone unauthorized is connected. I would change the Hotspot password, and keep an eye on your phone while using the hotspot. (Specifically, the blue banner or the control center that tells you have many connections are correctly active.)
I could be wrong, as I could not find any official documentation on the matter, and this is just my best guess