e.g.
https://github.com/commons-app/apps-android-commons/issues/2328
EDIT: Come to think of it, isn't Instagram owned by Facebook? It seems likely to me that this metadata is automatically inserted by the platform at the time of image upload. In other words, it may be a nothingburger. (Although the image itself is still very interesting)
Not may, it 100% does stand for Facebook Metadata, and you can easily interpret the data yourself.
https://medium.com/mindorks/reading-metadata-from-images-cbcdb0be6573
This was not an "embedded key" but may still have been a signal from a deadman switch. Just not as esoteric of a message as people would like.