Making a mistake doesn't revoke someone's property rights.
This is a non-sequitur, nobody is saying anything about anyone's property rights being revoked.
The teen asked for access, and the content owners, via the permissions they had configured, granted it. Sure they can later decide that this was a mistake, but that doesn't make it theft for the teen to have asked for access.
They made a mistake when configuring their web server. It's obvious that this was a mistake because some of the documents contained private information from Canadian citizens.
Per the tech article, it was an open archive of public documents that the government published periodically. The reasonable assumption is that the files were all public, and there's no reason to suspect the teenager in this case thought otherwise. The fact that ~3% of the files weren't properly redacted (whatever that means) is hardly "obvious".
> Making a mistake doesn't revoke someone's property rights.
Let's keep things constructive please.