I do not have ' Auto ' on a camea to check it out. I suspect it is a fixed program mode. I will do a graphic tomorrow to explain it, but in essence the camera takes a light reading and based on ISO selected determines shutter speed and aperture. The program will determine, some are fixed curves and others are depending on focal length set, a minimum safe shutter speed for that. It will then restrict closing down the aperture until that point is reached. If the light is poor the camera will just select a shutter speed to suit the light even though it falls below the determined safe point for that focal length of lens. It assumes the photographer is in control.
I would not worry about the Seychelles scenario as bucket loads of light there so this would not happen.
Don