I will be posting this link with absolutely no personal opinions or posts besides OP

The difference is in the intent. If someone purposely stored CP in cache then they would be guilty of possession. This decision at least allows for CP to be reported. There have been cases where people stumbled upon CP on the internet, they reported it to the police, then they get charged for possession because of cached images on their computer.

Indeed it is the difference. Most criminal offenses we're familiar with require intent for conviction. However, merely proving "possession" carries no such requirement. Certainly we can discuss whether that's the appropriate enforcement mechanism in the case of CP, but I think you'll find that proving intent for media, just like illegal substances, is quite difficult. It's why possession is the crime rather than (or at least, in addition to) use.

I'm just glad no one is trying to argue that this doesn't gut the possession aspect of the law.

EDIT: Okay that sounded wrong. Let me clarify.

However, merely proving "possession" carries no such requirement.

So, viewing CP is illegal. In addition to that, posssessing or distributing CP is illegal. In order to possess something there has to be intent, but in the case of possessing an image file on your computer, intent could be as simple as having your cache is set to retain things. That's enough to establish you had "intent" to possess the image files in your cache. So by having this wider definition of wrongdoing than viewing CP, it allows the state to achieve convictions in cases where they can't prove an obvious intent to use CP - which I'd argue is the majority on computers.