In the original timeline up to that point, I-Chaya did not die. However, that episode altered that part of history. Not necessary that anyone could tell, but does it really stand to reason that you could alter something like that and yet history goes exactly the same outside of the change?GUARDIAN: The traveller is returning.
KIRK: I sent the others up to the ship. What happened?
SPOCK: One small thing was changed this time. A pet died.
KIRK: A pet? Well, that wouldn't mean much in the course of time.
SPOCK: It might, to some.
If nothing else, it's food for thought, because I understand it's a TV show so some realism can be ignored where they don't want it in the narrative, but the butterfly effect is a huge thing in reality. You could make the argument that Star Trek thereafter really is a different universe.