Such a failure seems reasonable to me, such a pressure vessel obviously needs to be as light as possible to maximize payload. But making it lighter will make i

Such a failure seems reasonable to me, such a pressure vessel obviously needs to be as light as possible to maximize payload. But making it lighter will make it weaker. And even today there are limits to computer analysis, hence why they would do pressure tests at all; if the models were foolproof then why would anybody test pressure vessels? Pressure vessels are tested because their danger is well understood. Testing would be a waste of time if outcomes were certain, so failure during tests is not concerning. (This rocket falling over was presumably not part of a test to see whether it will fall over.)