Well,
@Hadron beat me to it.
I forgot I had an Instagram account; I had never installed its Android app, so I did that now. Then, when prompted to add a pic to my profile, everything became crystal clear!
As I said in
this post: IG doesn't know which gallery app you use; 'gallery' is a generic term for a collection of images; IG's "Gallery" that you're seeing may coincidentally have the same name as
your gallery app, but is likely displaying all the images on the device. Yep.
This is what I see when initiating uploading an image
using the Instagram app:
See the word 'Gallery' at the top? That's
not the name of your gallery app coincidentally named Gallery--it's a generic word for collection of images. As you can see, it automatically displays various images from my device.
Note the drop-down menu indicator right after the word Gallery,
the little, black, down arrow;
press it:
You're now able to choose images from any of the locations listed--which will be different from mine.
Mystery solved!
