That's not what copyright infringement is.
Docker runs the service and can do whatever they want.
If Apple sends a cease and desist, and Docker decides they'd rather take it down than risk going to court with Apple /to determine if there were damages/ - then they're free to do so.
What does this mean? If they could choose any course of action with no consequences they'd probably choose to do nothing.
Docker wasn't pushed into taking the image down, they *decided* that they'd rather take the image down than have a jury decide who is in the wrong.