Given that they were likely to be using similar depths because of sound transmission, and may have been using valleys in the Mid Atlantic Ridge - guesswork purely, but it isn't featureless down there, I suppose it may be more likely. The French apparently thought they had been brushed by a loose container - now that is worrying.

Twas in the broad Atlantic, the weather it was rough,
Two submarines crept slowly on, but were not quite slow enough..

With audience participation in the form of repeated pings - not appropriate in the real conditions, but hey...

Penny