I noticed they are now calling it simply "FTL" since it isn't hyperspace. I wonder about the specs on it now, like how fast it can go, what kind of FTL is it. Apparently it can travel pretty fast to get that far out there.
Actually, bear in mind that the ship has been out there for 100,000 (?) years. It might actually be an inferior, early form of FTL that "only" travels a few times faster than light. Over that span of time, a slower ship could have gotten that far, I figure.
Based on the visual effects (including the effect inside the ship when they dropped out of FTL) I wonder if it's the Stargate universe equivalent of warp drive, where a space bubble is being formed and squeezed before and behind the ship, thus there is somewhat of a red shift and stretching effect on visible light.
Potentially there's plot fodder here. For instance, it might be possible for an object (like a shuttle) to detach from Destiny while it's in FTL and transition to normal space once falls behind the "warp bubble" rather than being lost in hyperspace. By the same turn, it might be possible to more directly tract the Destiny while it's in FTL if you have the right technology or even intercept it before it comes out of FTL.
Also, just to throw it out there: if they ever gain some degree of control over Destiny, I'm going to say that a major plot that comes up will be Earth pestering them to try and catch a gate seeder ship that's somewhere ahead of them, because actually getting hands on a ship that manufactures Stargates would literally be the golden goose.