You do not know for absolute certain fact, which I know for absolute certain fact because the likelihood of your claim is incredibly low.
Are your friends phones running Android 5.0 or later? (I’m sure they are) they have RCS. End of story. This is not something you can dispute, you’re just wrong.
You can be in denial about it, but your friends have RCS.
Well I just bring it up because part of RCS is encryption, but there are a lot of asterisks and one of them is that RCS with Apple will never be encrypted.
It’s one of the main problems with RCS is that whether or not the chat is secure depends on the implementation and is dependent on sender and receiver, unlike iMessage where you know that when the chat bubbles are blue, your chat is encrypted.
IMO inconsistent encryption is worse than no encryption at all, due to the false sense of security.