Say a doppelganger tries to read someone wearing a ring of mind shielding- does it read what the wearer wants it to think or does the wearer's mind come across as a blank void?
While wearing this ring, you are immune to magic that allows other creatures to read your thoughts, determine whether you are lying, know your alignment, or know your creature type. Creatures can telepathically communicate with you only if you allow it.
This does not say anything about projecting false thoughts or even "your mind is an empty void"; it's just as if the magic failed for some other reason (saving throw, immunity to magic of some kind, blocked by the right amount of lead/stone/etc...). Someone trying to exercise mind reading just knows "I can't do it."