Is the desktop version of Instagram’s lightbox functioning the way it should? [on hold]

Most Lightboxes will allow a user to click out of the focused element and go back to the page.

However, on the desktop version of Instagram, once a user is done seeing a post, they need to click on the X on top right, as clicking outside of the post does not let you "out" of the post and back in the main gallery.

I'm assuming that it isn't "bad coding", and that there is a reason for it - track behavior, measure clicks... - but I couldn't find a statement on this matter, which seems counter-intuitive and less than optimal from accessibility standpoints.

Why is the desktop version of Instagram treating its lightboxes differently than most other lightboxes?