FHE involves adding random noise pretty constantly (FHE kind of works by adding noise at every step, and regulary does a magic encrypted re-encryption step where during evaluation the intermediate values are reencrypted without ever revealing the original value, to get rid of the excess noise).

Anyways, FHE is secure against (non-adaptive) chosen plaintext attacks. That among other things means that if E is the encryption function, E(7) != E(7), and if you have E(x) and E(y) you cant tell if x and y are related to each other unless you have access to the decryption function.