Yep, that was what went wrong.

Yes, he should have separated. Some engines failed to fire and lack of power caused spin and subsequent explosion. It could also be that they detonated it from the control center to prevent it from causing damage to the ground. The Starship has a bomb system that can be activated remotely. However, as I said before, they thought it would explode on the ground. There was little chance the launch would go well. This is only the first test. It was still a success!