You forget that Requiem is encased in a rather large metal shell… and Cortana was inside said shell when she said that.
Requiem has both an artificial sun to provide illumination for the shield world itself and its in the Epoch system orbiting the star Epoch, which is the star that destroyed the shield world, so both facts are accurate.
Or maybe, it orbits an ARTIFICIALLY MADE sun.
The star WASNT real, as it goes supernova when Requiem plunges into it.
Beautiful quote, but wrong star. Yes, the physics of the supernova are off, but the star Cortana is referring to is inside Requiem, like the other Dyson Spheres we've witnessed (Onyx/Trevelyan and the shield world of Halo Wars). While the star is not necessarily the center of the sphere, like the others, there are still "little" ones created for light. Also note that Infinity is still inside Requiem when Cortana goes into her quote.