Interesting. I find the Easyjet app is usually much more accurate for delays than the airport information, which often doesn't tell you of delays until you hit boarding time.
On one occasion at BHX, a Flybe flight was 'on time' until 'go to gate' time arrived, then suddenly a two hour delay appeared. As this was an internal flight, they would have known hours before then. A sternly worded letter at produced some compensation though!