This is because they didn't rebuild it or recode it or anything, they just took their ROM, made a PS1-SNES emulator (like the indie made SNES Station but of course theirs is the professional one) and just made the emulator run the rom, and thats it. Thats why FF4, FF5, FF6 AND CT lagged like hell.
Wow. Square soft was even lazy back then... Should of known.
And
the article(Everything in the darker green box), though it sounds very much like they are calling it a port, doesn't specifically say that it's just a port with a few added features. If you read it closely it says
This newly revamped edition maintains all of the game's original elements and spirit while
introducing the portability, dual-screen presentation and Touch-Screen functionality of Nintendo DS. Players will soon be able to rediscover the exhilarating RPG experience, breathtaking storyline and innovative gameplay in the palm of their hands.
Also
Remastered exclusively for Nintendo DS
They are being very vague about it... It doesn't say anywhere in the article that its a port(as in old graphics, sounds ect...). And, though I'm probably very wrong, it might possible maybe be a full blown remake. And while Kotaku calls it a port, thats just Kotaku. Maybe Square-enix wants us to think it's just an 'enhanced' port, just to suprise us and say "Oh yea, this is a remake.

"
... Wow even I realize how unlikely that would be. >_>; You know just forget it. That proves nothing... It's just a port with a new dungeon(Probably that Zeal prison they didn't add to the final version that was found in the beta rom or Singing Mountain, which doesn't even make it a new dungeon, just something they should've had in the original!) and wifi features(Probably trade your silver points with your friends for I-TEHMSSS!), just so they could sell it for $30 rather than just putting it on the Wii's virtual console and selling it for $8.
fuckin lazy assholes.

Edit: This makes me sound like an asshole myself actually. Don't get me wrong, I'm super happy that anything Chrono is getting released, and I'm happy that it's on the DS and not the PSP, but this is the only time I ever wanted a remake. It makes me kind of upset... After seeing how good Chrono Trigger could look in 3d from Chrono Resurrection, I would of love to see how it would look on the DS(Most likely something like Dragon Quest Monsters: Joker).