For flights over 3500 miles the delay indeed has to be over 4 hours to receive any kind of compensation. So if you arrive with 50+ minutes additional delay the compensation clause would apply.
The operator does not have to disclose why the flight was canceled, unless you would be filing a compensation claim - at which point they will most probably argue that the reason for the cancellation is outside of their control. Which in this case would probably be easy to refute.
Enjoy Easter in Greece! Kalo pascha
