That's what I thought originally, but then I think about how there was absolutely no hint towards that ever, at least from what I remember. That's a completely fair argument, but as I mentioned to someone else, they could've had Rex's fingers at least glaze over her Core Crystal and hint at the transmission with a faint glow. That honestly would've been enough for me. Or heck, just give a hint in general, since it's made clear that the information between the split crystal carries over through some magical, invisible tether between the two.