I don't think that "Lucius chose the exact same number as a stab against Dumbledore" is a very complex hypothesis. We already know that he knows part of the story and can reasonably assume he knows the whole story about Aberforth. So of course if the situation already demands that he hold someone on Dumbledore's side (sort of) for ransom for some obscene amount of money, on the assumption that it won't be paid, how could he resist rubbing that bit of salt in his nemesis's wounds?

It's not part of some bigger plan. It's not some fancy maneuver. It's just an emotional attack of opportunity aimed at Dumbledore, probably just for pride's sake.