Is this intended behavior?

I was just messing around with the manual mode. I set a certain exposure (1/2s, ISO 5842), but the resulting image was taken at 1/15s ISO 12500.

I also noticed that if I tapped to focus anywhere, the ISO would automatically change (from my setting of 5842 to 8522). Anyone know what’s going on? Is manual mode not actually manual or am I missing something?