Some iOS apps might launch in the background to refresh their data, or notifications briefly cause your screen to turn on. Screen Time will pick these up, even though you might not have used your device at that time. And while Timing tries to filter out these "bogus" activities, it can not always detect them with 100% reliability. If these entries bother you, you can always delete them from Timing's activity list: Click and drag onto the timeline to select the period during which these activities occurred. Then select the activities in question in the activity list. Right click them to open the context menu, then click "Delete".