I didnt at first either, until I realized that the Ent-J is massive in size. It's flat looking saucer section if I were to hazard a guess, would be 3-4 Ent-D's across. At least that's how I see it. Remember, it was leading the fight in the future against the Invading Aliens that created the whole Xindi conflict and The Expanse.I believe that is supposed to be the NX-01 Enterprise after she had been refit with a secondary hull.
I love this reel, but the "Enterprise J" (at 1:08) looks ridiculous: like a vinyl record with engines. I know it's how it looked in the ST: Enterprise episode; I just hate the design.
Man I want a model kit of that. Looks like it might have made the 5th season interesting and also explains the saucer design on all the starfleet ships.