The way l read it is as follows.
1. A/C departed late.
2. A/C returned to stand due Tech.
3. Crew then went out of hours or could not operate round trip.
4. Flight cancelled due to shortage of crews (no replacement crew avail), so it was not cancelled due Tech or 'extraordinary circumstances'.
5. If the airline concerned had enough crews on Standby or maybe even one crew on standby the flight would have operated.
Please pray tell how it is not the airlines fault.