[cvz]

Sharpening and bandwidth-limiting have the exact same effect, because the maximum sharpness of an image (like any other signal) depends on its bandwidth. There is no difference in the type of artifact produced. That's why the artifact from both has the same name of "ringing".

[astrange]

It doesn't come from "sharpening" at all though. That implies an increase in frequencies. This compression artifact comes from rounding them, so they're moved in both directions.