For what it's worth I looked at my reddit account and my hackernews account and they share one personality element in common. My perspective on this is that it's closer to cold reading type stuff - throw out a lot of traits, each of which applies to a lot of people, and then people will naturally find that a lot of what you've said applies to them.
Maybe another way you could test it is give it a day or two until you've forgotten what this website says. Then, write down a short description of yourself at each of the three stages. Finally, check three random accounts and see how much overlap there is between the random accounts and your self-descriptions.
Might also be that people present themselves differently on the two platforms. HN is more about professional discussion while Reddit is more about talking about hobbies.
Maybe another way you could test it is give it a day or two until you've forgotten what this website says. Then, write down a short description of yourself at each of the three stages. Finally, check three random accounts and see how much overlap there is between the random accounts and your self-descriptions.