The visceral negative response you get from, "Wait, I don't think that's right, it's more complicated than that", helps prevent speaking up the next time, unless you have an inherently disagreeable personality (which I cherish working with). I see it all the time with kids. They'll see some fundamental truth that takes a sideways perspective to see, and be told they're wrong, hacking off an interesting way of perceiving the world. It's unfortunate, but it's also something most adults are bad at, including myself.
And, I very often microwave my spoons, forks, even metal bowls, without them heating up at all. But I also have a basic understanding of resonance, absorption, insulation, apertures, and the wavelengths involved. I don't do it at work, because it's not worth the effort responding to "you're going to break the microwave", even if you show them that the food is hot and the fork is cool.
That said, I wouldn't melt metal in an expensive microwave. The metal has poor absorption relative to the magnetron antenna itself, so both will heat. I wouldn't be surprised if the antenna is also glowing a bit (at least early on)!