It actually was expected to do a flip and perform stage separation. It was a problem when it kept trying to flip and Starship didn't separate.
The explosion at the end was the Flight Termination System. In case of uncontrolled flight you detonate the rocket to keep it from flying somewhere dangerous.
From a PR perspective, I'm surprised that they don't have a procedure where they announce that they're considering to terminate, then announce that they'll blow it up, before actually doing it, if time allows.
I think there is a significant difference in public perception between "it blew up during the test" and "the test wasn't going to go anywhere good so they blew it up".
The explosion at the end was the Flight Termination System. In case of uncontrolled flight you detonate the rocket to keep it from flying somewhere dangerous.