UPDATE: Sling TV Support Response: @mikepland In regards to your inquiry, the user is prompted for this permission because the AP stores log files on external storage. *MD
Can an Android user explain what this means to me? Why does storing log files on an external storage device require access to photos? That makes no sense to a user.
There's only one external storage. And in an attempt (irony alert!) to make permissions "easy" for users to understand, some Android people decided to call the permission that grants access to external storage "Photos". Because that's where the photos are stored, and it's sometimes/often the most important/sensitive thing there.