Technically it sounds like you're a CA resident-- I think you just have to live in CA for 2 years for a reason other than to get an education. That probably means you should have been paying out of state tuition if you're at an East Coast school... Though I don't know how things would work if you're technically an in-state resident when you're accepted but out-of-state resident when you apply. Still, that's water under the bridge and if your school considered you in-state then go with that.
That being said, I don't think being a CA resident makes much of a difference unless you're talking about medical school--it doesn't make much difference what state you're a resident of when you apply for residency. Programs do often like residents they think will stay in the area and may prefer people who grew up locally, but they really just want the best candidates who will graduate from the program. Of note, many programs (especially smaller ones) may not think you're actually serious about their program if you're not in-state, so they may not interview you and give you the chance to express how interested you are in them. But a simple phone call to the program coordinator during application season usually solves that pretty quick.
Still, if you list that you're a CA resident, it certainly won't hurt your chances--it can only help (just maybe not much). But then it creates a funny situation where you're acknowledging your not an in-state resident, which may or may not be an issue. And you're really only supposed to claim one state residency, so if you're claiming residency in the state of your medical school, you shouldn't be claiming CA residency. (But as I pointed out--I think you actually are a CA resident).
I'm sure others may have a different opinion about all this.
