When faced with a line like this, does it always mean that the opponent has a strong hand or is he just defending his calling range, how do you react to this kind of action?

What do you mean by "Defending his calling range" ?\
Also, to answer your question, I think he's gonna have a mixture of bluffs and value hands.

From the little knowledge I have, my humble opinion is that you only make that play in case you have double pair, trio or more. Those situations would be of no use doing it to protect your rank, for courage or bluffing. In the case of doing so, you can be surprised or simply lose boats unnecessarily. In the event that that play has been made to you, I would first think about what the villain is like to know if it is a call or fold.