Active noise cancellation is just destructive interference. It doesn't fundamentally require any sounds to be bouncing off surfaces, and mechanical isolation would be passive noise cancellation.

The main caveat to active noise cancellation is that you cannot construct a destructive interference pattern that cancels the noise everywhere. Creating destructive interference to cancel out the noise at your ears will unavoidably mean creating constructive interference somewhere else.

see galaxy buds live, the only limitation is that active noise cancellation works up to certain frequency when passive cancellation must take over