A reasonable response
Preparing for a period of isolation is not the result of an extreme or irrational fear but rather an expression of our ingrained survival mechanisms. Historically, we had to protect ourselves from things such as harsh winters, failing crops or infectious diseases, without the aid of modern social institutions and technologies.
Stocking up on supplies is a valid response. It indicates citizens are not helplessly reacting to an outside circumstance but instead are thinking forward and planning for a possible situation.
While part of this response is due to the urge for self-reliance, it may also be a herd behaviour to some extent. A herd behaviour is one driven by imitating what others do – these behaviours can be a kind of conditional cooperation with others.