I was as surprised as you to hear this, but from what I heard the ride will not be ready by October. They said it's more complicated than just cloning the ride—different building codes and other technical stuff like that. This was on a time-limited Zoom call and they were being very careful not to say much. I wanted to say, "Hey, that doesn't make any sense! It looks totally done from all the photos I've seen!" But that would have been a bit rude to someone who already was telling me more than they probably should. So I don't know, I think I trust what they're telling me. There would be no reason for this person not to know what was going on at the work site.
I agree, though I definitely got the indication that the inside is also not done.
Here's my more-educated-than-usual guesses (piecing together what my source told me):
OPTIMISTIC: at D23 they will announce that TRON will open in mid-December 2022 (during the holiday season, they'll keep Splash open until mid-January in this scenario). This is supposing that no further issues come up while they're finishing up.
PESSIMISTIC: at D23 they will announce a Spring 2023 opening for TRON, which will at the worst mean May 2023 a la Guardians. I can't imagine this happening, but if what my source says is to be believed, there's still quite a bit left and this would have to be the farthest limit.