Someone above mentioned that magnetron bombarded by another magnetron can cause a feedback loop thus causing the explosion. I am not exactly sure if that is scientifically correct but that could be one explanation for the explosion.
But yeah the rest of the story is probably just a meme story.
Microwaves are not to be fucked with. Microwaves are produced inside the oven by an electron tube called a magnetron. The microwaves are then reflected within the metal interior of the oven where they are absorbed by food.
When a magnetron bombards another magnetron with microwaves it produces a feedback loop that can result in an explosion. This phenomenon was first recorded in 1998, the same year that The Undertaker threw Mankind off Hell In A Cell, and plummeted 16 ft through an announcer's table.
Placing a bag of holding inside an extradimensional space created by a handy haversack, portable hole, or similar item instantly destroys both items and opens a gate to the Astral Plane. The gate originates where the one item was placed inside the other. Any creature within 10 feet of the gate is sucked through it to a random location on the Astral Plane. The gate then closes. The gate is one-way only and can't be reopened.
The explosion destroyed both microwaves and created a portal to the astral plane.
Jokes aside, the magnetron is just a vacuum tube surrounded by a big heatsink. It could implode but the vacuum volume is tiny and the metal inside and outside will prevent glass from flying everywhere, unlike a B/W CRT. There is also a transformer, HV capacitor, fan, a tray motor, a mechanical or electronic timer, lightbulb, high voltage diode and fuse, bimetallic contactors (thermal fuses), safety switches, interference filter and smooth start circuitry.
None of this can really explode but will get hot in presence of microwaves, burning plastic and other materials, producing caustic smoke.
Oh, and I forgot the most dangerous part: the magtrometer, which can easily explode.
This is clearly nonsense. Besides the fact that you can't fit a microwave inside another microwave, microwaves don't explode.
Let me say it again, microwaves don't explode. This is obvious.
The lack of basic education that some countries have on common household items such as microwaves is shocking.
It's as if they teach their school children nothing but abstract concepts for 13 years, and then send them out into the world without understanding how a microwave works, or how electricity works, or how a computer works, or their nation's laws and their rights as citizens and workers, or... anything, really.
For all that education, people seem to leave school completely unprepared for the real world. They are let down by the system. It's sad to see.