The outside air quality (on the bottom of the app's home screen) comes from an air quality monitoring station near you. These stations are big machines typically run by government environmental agencies. We show the outside air quality if the there's a station within 9 miles (15km) of you. Generally, what you see on the tracker outside and what the monitoring station shows should be fairly similar. But, often times, these stations might sense something a bit different than what your tracker senses right outside your building, due to air quality microclimates. For instance, their might be an industrial plant near the monitoring station, or there might be an exhaust-filled highway near your backyard.
If you believe that the value coming from your tracker is egregiously wrong, then please refer to this Wynd Help Center article.