What is the "maybe" caller id suggestion in the call log based on?
iOS scans your email for contact info.  If the phone number is not in your Address Book, for matches, it looks to your email to see if anyone with this number sent you email.  If it finds the phone number associated with a contact from your email, it will show you "Maybe:" with its guess of the person's name.

You can disable this feature, if you want, by:


Go to Settings --> Mail, Contacts, Calendars
Under Contacts, toggle the switch labeled Contacts Found in Mail to the OFF position