While this is a fairly good explanation of application, the details are technically not really true.
25V/70V/100V is not a measure of impedance but a description of what would properly be called a level of “constant voltage” amplifier output, and actually the true impedance (which is measured in Ohms, not volts) can vary considerably in constant voltage systems, depending on the actual physics of the system’s components and the real amount of resistance introduced by them.
The real physics involved can be fairly complicated to explain thoroughly, unfortunately, which is why the descriptions tend to get simplified to 8-ohm vs 70-volt for ease of communication. The true measure of impedance still comes in to play in constant voltage system designs but is expressed in terms of total speaker load wattage versus rated amplifier output, which makes them easier to design, as the math involved is much simpler than in a low-Z system (CV speakers have on-board transformers that convert the applied power to be appropriate for the driver). At the installation/troubleshooting stage it can be extremely important, hence an impedance meter should be used in CV installations to ensure there are no faults, etc