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.
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.
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.
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.