Some facts. Yes, facts.
1. The YouTube clip is heavily edited.
2. The amended clearance to the Stobart ATR was partially blocked, crucially their callsign was blocked. This IS captured in the YouTube clip, and was also confirmed by DUB duty ATC manager to the ATR Captain later that evening after the tapes had been reviewed in the ATC listening room.
3. Because the amended clearance to the ATR was blocked it was never acknowledged by the Stobart crew, and as such the initial "subject to RYR" remained their valid clearance.
4. The BA took 5 mins to commence pushback, by which time the Stobart was well underway.
All facts, all verified.