Question about aliasing
What you describe is indeed aliasing. If there are frequency components above half the sampling frequency then they will be folded back to the interval $[0,f_s/2]$. This folding back is called aliasing, no matter whether these aliased components overlap with other parts of the signal spectrum or not.
Note that you can also use aliasing to your advantage if you're careful that no overlap occurs. An example is bandpass sampling, where you deliberately choose a sampling frequency that is much smaller than twice the highest signal frequency.