The first flag was 54-by-28-inch vs the second being 96-by-56–inch.
The news of this wish did not sit well with 2nd Battalion Commander Chandler Johnson, whose temperament was every bit as fiery as Howlin Mad’s. “To hell with that!” the colonel spat when the message reached him. The flag belonged to the battalion, as far as Johnson was concerned. He decided to secure it as soon as possible, and dispatched his assistant operations officer, Lieutenant Ted Tuttle, to the beach to obtain a replacement flag. As an afterthought, Johnson called after Tuttle: “And make it a bigger one.” — James Bradley, Flags of Our Fathers
https://en.m.wikipedia.org/wiki/Raising_the_Flag_on_Iwo_Jima
They also wanted a video of it happening and the flag was already up before someone arrived with a movie camera.
The original flag raising was only photographed. So when you see the video, that’s the reenactment with the larger flag.