Technically, yes, it is encrypted. However, Facebook still gets metadata on who you talk to, when you talk to them, how long you talk to them, your contact information, etc. As an example, if you talked to your girlfriend, then you talked to her doctor, and then you talked to your mom. There’s a good chance that your girlfriend may be pregnant, even if I did not know what was said. Or, if I know you are at the top of a bridge and that you contacted a suicide hotline… So just because it is encrypted does not mean it is safe.