It sucks for their users who maybe don’t know the golden rule above. I certainly don’t blame non-tech folk who paid a known photography company to handle a complex problem on their behalf - they did the right thing in handing this responsibility to people who they believed could be trusted.
To the greater point - this is incredibly damning of Canon’s cloud storage going forward. As others have said, the amount of data lost overall is not much in the greater scheme of things, but that’s not the concern. What’s worrying is that they were able to lose any data at all. How much redundancy do they have? How are permissions managed?
When I backup photos and videos at home I have a script to chattr -i all the files independently as they’re stored on top of the redundancy and backups. You need to protect your data from yourself, too.