the two accounts were not linked in any way [email address, openID, et cetera] except for having the same name on record.
Having the same name on record had nothing to do with it. Yelp was forwarding the information to a page on Facebook, which used the cookies stored in your browser to see which account was logged in (same as how when you log in to Facebook, go elsewhere online, and then return, it knows which account is logged in and doesn't ask you to log in again).
That aside, you've got it right. The problem with Beacon (in it's original implementation) was that it did unexpected stuff without the user's consent.