Microwaves have never, "required" containment - it's an efficiency thing more than anything and that's one of the main reasons as to why they're present in household microwave ovens.

You could have attended that event all day long but that doesn't change the reality of how RF works. You're not going to get something that can penetrate a tank at any significant distance where it can cause any immediate effects to the person inside the metal tank. It's a fundamental lack of understanding of how energy propagates.