Forgot to remove sim card and possibly sign out of icloud before selling!
If you did a "Erase All Content and Settings" - then you have definitely logged the device out of your iCloud account. This function deletes everything stored on the phone, including accounts, app settings, app data, the apps themselves, documents, photos, etc.

If you had "Find My iPhone" enabled, the buyer of your phone would not be able to setup the phone without entering your username and password. I.e. they would have complained to you by now that the phone is essentially bricked. As weeks have gone by, it is far to assume that you either logged out of "Find My iPhone" or never had it enabled on this phone.