I think that might be the out that takes them into next season - that didn’t ring true at all. I haven’t figured out why Red John would have been saying that, though.
That would make a certain amount of sense; it would be very like Red John to mess with Jane even further - turning him into a murderer, and having him thinking that he killed the man who murdered his family then finding out that yes, he technically did, but the mastermind behind all of it is still alive.