Based on public information from the university this shows real-time data of whether a place is busy. Working off 5 months data, the predictions of when to go to the library are based on historical data.
The colours representing whether a place is full, busy or free should be completely accurate. The % availability is more to show the trend of availability rather than the actual amount available. The predictions (for tomorrow, later today) are being tracked and compared with the real data to help improve them over time.