One non-obvious step I encountered. After login with LinkedIn, it doesn't look like you logged in but you did. You have to hit the "Explore" button on the top bar and then you'll see your name menu on the upper right, and you can proceed to settings.
Another thing: if you've never directly used Slideshare and instead signed in via your Linkedin in username, you'll need to set a password in order to delete the account (it prompts you to set one in the delete modal).
<shrug> Their site is so full of anti-patterns it's quite possible I accidentally signed up again and deleted again. Either way, it wanted a real password before letting me click delete.
How do we know that clicking the "Login with LinkedIn" button doesn't create the account? OpenID Connect/oAuth logins all work the same - if you haven't already signed up, "logging in as <x>" creates the account for you.
To answer you, the account was associated with my real email but had no password. Saw after deleting the account because it sent a deletion confirmation to my real personal email (that it should never have had in the first place).
To answer the parent post, OAuth doesn't automatically associate accounts. The first time you login (signup) to something with linkedin/google/facebook it gives you a popup warning that you're about to authenticate and share data with a third party service, please confirm.
If you see that popup on login, you don't have an account, don't proceed.