Why couldnt they just say due to ATC changes on the route or headwinds!
Perhaps because the captain knew that blaming ATC or headwinds would be dishonest ? Had the situation turned more serious and warranted landing somewhere in France, anyone performing an investigation as to what had happened would want the captain to explain the nature of the stated ATC issue if there was no evidence of one !
One doesn't always have to say something - but if you do say something, it had better be correct.