Does the WWW class do anything in the backend to check if there is an open internet connection before it tries to load anything? If it doesn’t, what is the timeout like before it stops trying to load (if it even does have a timeout)?
@anon_1871033 's post is very old, but still no answer - I would also like to know the answer to this mystery!
There is no built-in functionality to do that in Unity. You need to implement a system to send an HTTP request to a known page and get the response. If the response is the expected one, then you are online, otherwise you are not. Take into account that some networks are connected but restricted (hotels, airports etc), therefore the “actual” internet is still not accesible.
If you don’t want to implement that on your own, I have created the asset Eazy NetChecker which handles all of that, including a custom editor and custom server/page checks. It is not free but it is super cheap.