So they told you that’s not supported and don’t do it. You then did it and seem surprised at a bad outcome. And you’re blaming the software and/or vendor?
The proper way would be to abort the upgrade upon discovering that I am going for an unsupported way.
This is not serious software.
If you don't support upgrading, don't expose that in the UI. There's no excuse for having UI that will let the user do something unsupported and then screw up their data.
Besides that, it is unethical and I wouldn't want to work at a company that pulls such stunts. I think a lot of people wouldn't. It'd be hard to keep secret, too, I mean, 5 years later the employee that was asked to do it works somewhere else and BOOM.
So all together, I think it's extremely unlikely to happen.
I CAN imagine a disgruntled ex employee or angry employee at a competitor would pull something like this. We have seen employees at a competitor create social media sock puppet accounts to spread FUD about us - but management at the competitor put a stop to that once we notified them.