Was the original shot without HDR ?
and, if so, are you saying that Apple is (automatically) applying a +4EV (a clandestine exposure correction ) boost ?
How exactly the DNG file was built only Apple knows, but for sure it was made from at least 2 shots with different exposure. I guess HDR is activated by default like in most modern smartphones.
Not sure if I understand your question about the +4EV, that is just a metadata value:
D:\iphone\ej1>exiftool -baselineexposure iphone.DNG
Baseline Exposure : 4.009187698
It informs the RAW developer to apply a previous exposure correction, otherwise the image would render very dark.
Regards