Intro to Fully Homomorphic Encryption

If Enc(2) + Enc(3) = Enc(5), and Enc(1) + Enc(4) = Enc(5). Does Enc(5) represent the same ciphertext in both cases? I'm asking because, if so, shouldn't it be trivial to uncover the plaintexts if you can perform any math op on the ciphertexts?

The author touched on the performance problem but is anyone aware of homomorphic encryption being used in the real world today, outside of academia?

This is only a "Gentle Intro" if you know advanced mathematical notation.