It's working as intended - the % displayed is relative to the forum's average activity.
Let's say your average user generates 50 activity points a day. This is then set as 100% of the daily activity target. If you gain 100 points, you'll show as having earned 200% of the daily activity target.
You can adjust what the baseline of the activity target is by modifying the "Minimum Points" setting in the Activity Stats options, then waiting for the scheduled task to run again. Do not modify the "Activity Target" setting, as it'll be overwritten the next day and is only used for illustrative purposes.