More like the odds of two 747's colliding and not knowing it happened.
Pure nonsense.
Read the article. The French were well aware that they had git something. They just didn't know what. The only way that you would know is if you heard it before or after the crash. As its sonar dome was damaged, that leaves only the before part.
A better question would perhaps be to ask how the British knew what they hit, but didn't avoid it.