And yep, it was 100% triggered by a slight movement to the right while holding finger down anywhere on the left edge in the main feed. And it happens even if you just move it by a few pixels, to the point where someone else looking at the screen might not notice.
As someone else has already pointed out, OP can just revoke camera permissions from instagram in the phone settings. The app will still fully work, and will just ask for camera permissions if you attempt to use any features that actually require camera access.
P.S. I feel it is rather difficult to trigger accidentally though, and I am saying it as someone with large hands/fingers. It happened to me before a couple of times over the years, but I've noticed instantly, and not because of the camera LED lighting up. I've noticed because the entire rest of the UI becomes unresponsive (e.g., scrolling up/down doesn't work) until you release the "swipe right" gesture hold, which makes perfect sense. So you cannot really stay in that weird state, unless you are committed to holding your finger on the screen in that spot without moving or releasing it.