I smell an urban legend.
No first hand experience, only one company response, and even then, not a dominant builder of the product, Friends of Friends, unnamed alleged reliable sources, descriptions beyond science, fixes that are self contradictory and so on.
OK. First, to superheat water requires higher than normal pressure. A microwave is not a pressure cooker. It won't and physically can't happen. Microwaves aren't magic. They are very well understood. If the microwave was high pressure, The door would have blown out of his hand as he opened it and the water would have erupted out of the cup then as the pressure changed.
Second, cups and other common microwave items are flawed, They contain imperfections that cause liquids to bubble before they are technically at the boiling point. The liquid will certainly bubble. This is even before the scratches are taken into account. Surfaces are inherently imperfect. High school science teachers as authorities? Please. More on this in a bit.
Third, oven variances. Manufacturer and power of the oven isn't known. I have two microwaves. In the older low powered one, it takes about 1:45 to boil 1 cup of water. Sad, isn't it. In the newer one, 1 cup boils in about 40 seconds. It's much higher wattage too.
Fourth, Heat behavior. The science teacher's explanation is wrong. Thermodynamics is well understood. Look at the explanation. Bubbles release the heat? No. Water has a clearly understood reaction as it transitions from water to steam. It takes a known and fixed amount of energy for this to happen. The water will never pass the boiling point in temperature as long as it is liquid under normal pressure, which we have established as normal in the microwave. The water will continue to absorb energy to convert molecules to the steam state, but the temperature stays the same. This is why a steam burn, even though at the same temperature as the boiling water, is much worse. There is more energy in steam to burn you with.
Fifth, logic and the law. The person who had the accident does not verifiably have a GE oven. Why does an unaffiliated person write to GE for an answer on an unknown product? Why would GE give instructions on a product that wasn't theirs. They wouldn't. Corporate liability and lawsuits would destroy them.
Bogus through and through.