Even if I had booked back to back, I don’t see how the point made is true: the flight to BOS originated in Amsterdam. My one way trip to AMS would be a separate ticket regardless, would it not? Even if the outbound had been cancelled, the new flight wouldn’t be cancelled.

City to Rotterdam the next morning at 7.45 was no good because I’d have missed my flight from AMS to LHR at 7.45.