Yeah, you basically reverse-engineered something there. Good job!

For the average programmer, it might not seem too much. But for a normal user, seeing something and figure out how it's working, without knowing internals beforehand, can be said to be reverse-engineering.

I guess we should start rating reverse-engineering so people can know what to expect.

I think he just showed us what is insecure direct object reference and not reverse engineered anything. Both op of your comment, and one from the post.