Instead of clicking the "login" button on discord's home page, you clicked the "Open discord in your browser" button.

This, by default if you're not logged in, takes you to a create account flow. The prompt you entered your _username_ into was the "Pick a display name" prompt. If you enter, say, "user" it silently adds numbers to your displayname to make a new username ("user1234"), rather than redirecting you to the login page or prompting you about it (like most other sites do).

At the end of the flow is a "Finish signing up", "claim your account" prompt (which really is the end of the "create a new account" flow, the ephemeral account without an email you're using there is in a partially signed up state).

This is the box where you were entering your email, getting a conflict, and ended up using a new email to create a totally new account.

I know people who use hacker news are on-average much less tech savvy than the average discord user, so I can get why you missed the login button on the home page and instead went through the "create account flow", but everything that happened is "working as intended" rather than a "bug".

I do agree the flow there is pretty confusing. They've managed to make the new user signup flow so optimized you didn't even realize you were doing it.

Still, by the time it was telling you your email was already registered, you really should have slowed down and noticed it was telling you you were creating a new account rather than using a new email address for some reason.