He left it open to interpretation and that's always a mistake, same thing with Cerny not specifically saying "hardware accelerated ray tracing" when originally talking about the PS5, most people jumped on that and acted like it was going to be software based because he didn't spell it out. As it turns out it is hardware accelerated ray tracing in the PS5 but people argued about it for a while.
Phil saying twice the performance can mean literally what he said which actually isn't 12TF or he could have said 12TF which would mean 12TF for the type of GPU they are using, we'll find out soon enough. Like I said before it's going to be very powerful regardless of what the final TF number ends up being and people shouldn't be disappointed if it's in the 10+ range when all is said and done.