While I was not there I can provide a possible explanation on the matter.
Awhile ago it was decided if we went into a fight where both are enemies of our own faction we would not shoot the faction with less ships, if the Bretonians were outnumbered then it is likely that they decided not to make a bad situation worse for them and simply attacked the 'stronger side' in the spirit of 'fair play'. Though I would've preferred it if they used Bombers. -_-
This policy was brought in during the Gallia/Bretonian fights and has been in place for quite some time now. I hope this helps you out Jack and assorted peoples and remember this does not mean we are allied, merely taking care of the bigger threat that would otherwise completely crush us after the fight is over. Still hate yer guts filthy Imperialistic dogs.