Decrypt with FileVault
No, your disk is decrypted when you turn off FileVault.

From the Apple Knowledgebase:


  When you turn off FileVault, encryption is turned off and the contents of your disk are decrypted. The decrypting of your disk could take a while, depending on how much information you have stored. However, you can still use your Mac to do other tasks while the decryption is occurring.


It could be that FileVault was still decrypting your hard drive while you were running Mac Booster.