I think in order to pull off the 'one race win', you have to like get rid of all the others, not simple, but i think that is how chris said it plays out with one.
Yep, that's about how it works... but... good luck trying it and not getting yourself wiped out in the process....
Yep, exactly. And it's not like "you" can just directly do whatever. None of your direct actions can destroy a race. So you have to engineer one race killing the last of all the others, but not you, while already being in the federation, to win. You can't form a one-race federation, either; so all the allies of the race who WERE in the federation have to have already been killed, too. So that's doubly hard, because races in the federation will support one another. That means that your target race has to have been fighting a foe who was superior enough to overcome the entire federation EXCEPT that race, and then that race turned things around and won.
Of course, your hand would be evident in that from start to finish, but still.