Yes, the 'z' in hi-z and lo-z cables is the standard variable name for impedance (like 'v' for voltage or 'i' for current). 'AC' in this context means 'not DC'

Yes, the 'z' in hi-z and lo-z cables is the standard variable name for impedance (like 'v' for voltage or 'i' for current). 'AC' in this context means 'not DC', which is to say 'varies over time'. Instrument cables certainly qualify under that definition, though it is definitely confusing to call it 'alternating' (which we normally think implies 'goes back and forth between 2 states'), where perhaps 'varying' or 'time-varying' would be more appropriate.