[user5994461]

If you don't have an account, you shall get a popup from LinkedIn warning you that you're about to sign up and share data with a third party service (a standard oauth form you also see with Google/Facebook/GitHub auth).

If you get the popup, by all means, do NOT confirm or it will create an account. Haven't heard of people getting the popup though, strong hint that all users were magically autocreated.

[sseneca]

Yes I didn't get a popup either time so I'm assuming that LinkedIn, in their infinite benevolence, automatically created an account for me.

[rvanlaar]

I did get a popup, but it was automatically closed before I could interact with it.