I could not explain why one sub in one experiment did what it did. I can tell you that I installed car audio professionally for over a decade, and I have seen many blown subs for many reasons. Usually it was the customer playing with the gains after leaving the shop.
Subs will blow in one of three ways; open voice coil, fused or swelled voice coil, or mechanical damage, which can include torn spiders, voice coils that have jumped the gap, etc.
An open voice coil can happen from too much or too little power, or just bad luck. A loud bass beat or even a bump in the road can cause a voice coil connection to fail at a terminal, or where the lead in wires meet the cone, or anywhere in the electrical path. It is not always someone's or something's fault.
A swelled voice coil means it got too hot, this can be from sending far too much power through it, but is more common from sending clipping/distortion/DC through it, and this is most common from too little power. Once again, forget rated power because a speaker's power handling depends on many things, including its enclosure, the type of signal being sent to it, crossover points, etc.
If a sub is pushed so hard that the voice coils hits the bottom, or actually jumps out of the magnetic gap, that is from too much power, but I would say that it should not come as a surprise to anyone because it would have been so loud and so distorted that they should have heard the damage coming.
To use an example, my $39 POS 10" sub has been running on an 800W RMS amp in my vehicle, and it is on its 4th year without a problem. A rule of thumb I used when installing and setting up car audio systems was that if you can hear distortion, you are doing harm to your speakers, and you can hear much more distortion with too little power. If you want to see how quickly DC can end a speakers life, you can hook up a 4 ohm sub to 36 watts of DC by connecting it across a car battery terminals. Dont try this unless you are planning to throw the speaker away, cuz it will be dead very quickly.