The initial news article out of Dallas yesterday stated that the propeller broke loose just after the P-51 lifted off, while the pilot was still over the airfield. The pilot didn't have enough time to get the gear back down, just dead-sticked it onto the grass. Could've been a lot worse.
It looks like he did try to get the landing gear down, the tailwheel is down in the pictures, I guess he did’nt have enough altitude to lower the mains.