Your exposure compensation is in the partial metering mode.
Just point the center spot at what you want protected in the image and grab a reading.
The camera will still take some amount from the rest of the frame and the spot is rather large.
To Canon statement only this indicated area is metered in "partial" mode, not the rest, they even state the area of this metering patch . You can check at your sample with a light-spot in rather dark surrounding.
The kind of opposite is the "average" mode, which is integral, but center-weighted.
And as with most cameras from that period any other correction is to be done at the ISO setting.
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