Legalities aside.
When youre at an airport waiting for a connecting flight possible with family and kids plus with hotels and tours booked, and to be told your flight is cancelled , i can understand paying the high price for another ticket and just so you don't miss out and thinking "ill sort it out once i get back home"
You could sit there and demand compensation and Chuck up a stink but for every hour you take the chances of not gettinf an alternative flight is too risky
Which isn't the case in what we're talking about.
He was contacted in February, about a flight in April, and only confirmed his acceptance 10 days after he was informed/offered choices. No urgency in the timing of the situation like you described, as being mid-travel.