What you are seeing is contacts in the "Collected addresses" in the Address Book. This function will keep email addresses and names of anyone you send an email to or receive one from, even if they are not in the address book. You can disable this if you want to by clicking on the gear icon in the upper right corner of the page when in the Inbox, then on Settings. Under Mail Settings>>>>>>>Common, you will see the options. If you only want to delete some of them, go into the Address book, then click on "Collected addresses" in the left pane. There you can make the deletions.
Latoque has provided some great advice! Please let me know if this solves your issue or if you are still having troubles that I can assist you with.