To put it another way; Fleet only kicks in when the game ends. By the time the game has ended, it's reasonable to think that you must have already dealt with any Outpost turns (and those rules say that such turns are dealt with by never happening). So it takes a special ruling like this to conclude that any player having a Fleet causes a last-turn Outpost to now work.
The way I see it, Fleet does not 'reopen' an already ended game, it implicitely changes the rules on when and how a game ends. What were previously absolute game ending conditions now become conditional ones. If no player has bought Fleet, they still end the game immediately. If a player has, Fleet generates one or more exrtra turns, that mix with other extra turns, either already existing or created later.
What irritates me at the moment is that the rulebook explicitely calls out the order of the extra fleet turns. Normally the rules handle this already, so I'm unsure if this is a restatement of the normal rules for extra turns, made under the assumption that the turn triggering fleet was a non-extra turn, or something new. It isn't the 'normal way' either, as after the 'game ending turn' normally any extra turns for that player would come first, while the intention is obviously that that player is last in the Fleet turns (if they have bought it at all).
Test case: 2 player game, my oppoennt has bought Fleet, I haven't. I play Possession and buy the last Province, so Fleet kicks in when this turn ends and creates an extra Fleet turn for my opponent. Now there are 2 extra turns for my opponent: 1x Possession, 1x Fleet.
Is opponent able to choose the Fleet turn first, thus ending the game before I get to possess them? I think they should, but I'm not sure.