The combination of ISO 80 + f4 against that moment EV value, need slower shuttle speed to get enough light to obtain a proper exposure. As 1/400 is too fast yet allow only enough lights to reflect from the plant but fail to capture enough lights from the background. Thus the background is underexposure thus it is black.
I ever experience this using flash at a very fast shuttle during day shoot too. Sometime I purposely do it to get rid of the ugly background.
The flower is under the bright sun light.
The background is the building in the shadow.
I was aiming my camera upwards and zooming at max 12x.
Exposure correction -2/3 in P mode.
Of couse, no flash.
EXIF file is intact. Can check out the date and time as well.