Yes, there is a bit of disconnect there, if he had never told anyone Tori would not know that he had been accepted before.
I don't think it's that much of a disconnect, just takes a little bit of assumption. Upon seeing the movie the first time, my brain did this in about 5 seconds:
1) Zach gets into CalArts, his dream come true that he turns down because he feels the familial obligation.
2) Zach doesn't tell any of his family.
3) Zach doesn't tell his best friend Gabe, who may not understand the situation and would give biased advise, perhaps something similar to what Shaun says earlier in the movie ("You don't have to. It's a choice.")
4) Zach tells other best friend Tori, because she will provide a different perspective than Gabe. ("You are so responsible, please make out with me!") He asks her not to share this with anyone. That she isn't confused by Zach's re-acceptance supports this theory.
5) Zach tells Shaun, "I never told anyone," which is merely an exaggeration. After all, it may be poor form to mention how he confided in his ex-girlfriend while trying to share an epiphany with his new boyfriend.