Is it possible for the ex narc to call out of the blue acting like someone completely different even if they did the discard? 

Most definitely. They are always playing a role anyhow and it really doesn’t matter if they did the discard. When they want supply, they will circle back around to see if they can suck more out of you in one way or another.

They are acting like a completely different person either to prove something to someone else listening or because they believe that is who you want them to be, so they will mirror it to pull you back in.