Were xenon lights not invented pre '97 then 
Matters not, HIDs and Xenon are completely and totaly different ....
Xenon is a gas, and can be in a bulb of any voltage, just like sodium, helium, halogen etc etc etc that will prevent an incandescent light (glowing filament) from oxidising and going "pop" .. they are still filament bulbs. The use of xenon gas as a protector allows the filament to run hotter thus providing more white light ... the filament is "white hot"
HID's are High Intensity Discharge lights that work off a high energy (voltage) to "strike" an electric arc that gives off the light, the fact that the gas in the "bulb" might be xenon is by-the-by but is what causes the confusion.
So you can have xenon bulbs that work off 12 volt and the gas just protects the glowing wire, or xenon HIDs where the gas is an inert vehicle to contain the electric arc running at thousands of volts and help form the "plasma" field that makes the light
HTH
EDIT
For those who wish to understand better ...
https://en.wikipedia.org/wiki/High-intensity_discharge_lamp 