Tube shorts test is a standard feature of most tube testers.
Guitar amps will likely see a fair bit of handling. Tubes do not handle impacts well. Internal structures have spot welded thin wires.
Modern solid state equipment is very rugged in this aspect and young people may not be aware of how fragile tubes are.
Careful with the generality. The first missile system I worked on had vacuum tubes. We didn't worry too much about the tube's lifespan
The ability to handle shock is dependent on the type of tube. The tube in question is not specifically rated for shock. I rebuilt my first guitar amp in the late 60's. I have seen a lot of abused amps, but the only times I have seen multiple tube failures (other than power supply failures) was when the amps in question were clearly crashed, or burned, or fell out in shipment (but the tubes usually survived unless cracked).
If one was to make a sweeping generality, though, I would make the reverse claim
Tubes can take a lot more abuse than solid state devices. I know this because for the last 40 years, I have designed and manufactured solid state devices (transistors, diodes, ...). I have seen far more premature output transistor failures than output tubes (without obvious reason of course).
My dad, step-father, grandfather, and all 4 uncles flew planes in WWII, packed with vacuum tubes. The only failures they had were due to shrapnel and bullets.
I have generally had good luck with JJ tubes. The specific shorts on these are not unusual, for beam-forming pentodes, where the beam plates are internally tied to the cathode (pin 8). Screen to screen shorts happen, especially in tubes that are not frame grid types. It is not unheard of for a broken screen wire to be touching the beam plate. One of the two screen wires has a bad break and swings loose to get tangled with the other screen and/or the beam plates.
This may have been shock but it could also happen if the screen resistor fails. Which came first can be hard to distinguish. Fenders were notorious for killing tubes this way. It was not the fault of the tubes though. I loved Leo but he was a tight-wad!
-grego