The percentage you see there is the percentage used by the Play service since you have last (fully) charged your device. If you would charge your phone, unplug it and immediately start using the Play Store a lot, it will (and should) display a high percentage. Same thing goes e.g. for a game. Let's say 1% of your battery has been used by Play while 2% of your battery has depleted. Play will show as having used 50% of your battery. If continue using your phone, but not Play, and get down to 90% battery, Play's percentage will go down to 10%.
You see only a snapshot of your battery use since the last full charge, it does not mean anything beyond that.
Although you can't compare it, mine is at 8% since I was downloading some apps earlier. While typing this it went down to 7%.