OK, suppose the police find out that a CSAM image was posted on a forum. About an hour later it was deleted by the mods, but in that time it was unwittingly viewed a number of times by users of the forum who had no idea it was in that thread. Some users didn’t even scroll down far enough in the thread to actually see the image, but it still got grabbed by their web browser, because the browser loads the whole page, not just the part you’re looking at. Now suppose that you are one of those users.
Now the cops subpoena a list of every IP address that downloaded that image, tie those IP addresses back to specific users. Now you get your door kicked in by the cops looking for evidence of child porn stored on your computer. And depending on various other factors, they might even still find that image stored there in some form, without you having any idea about it.
This is why it’s important to understand that there is no technical difference between downloading and viewing. Your lawyer’s job is now going to be to prove that you never wittingly chose for that image to be delivered to your computer, even though it absolutely was delivered there as a direct result of actions you took. Your web browser made the request to the server to send that image to it, because you made the request to open that page. So there has to be more than just the technical action of “downloading.” There needs to be intent.
Now in this case, there clearly was intent, given that the image was viewed multiple times over two years. But that’s important context that is needed on top of just the fact that the image was downloaded.