There are no cheats in Halo what so ever and even if he used the trainer which gives unlimited ammo, life and loads of other stuff it doesn't mean it's exclusive to him, you're also going to have the same advantages as him.
One thing he must have done is that he probably increased the health to 400% which is why it takes longer to die.
About you dieing quicky, well he must have gotten better than you because you have equal advantages.
If your still in doub, play on your xbox and see who wins.