Just wanted to let you all know, today I decided to call Disney Dining personally to double check on this issue. I was told there is no special dining event for 7/4 at Cali Grill and that my ADR is intact. She was also able to modify my reservation and change it to 3 people instead of 4. She mentioned that we would have been charged for the 4th person if we hadn't made the change. So glad I asked!
I'm very happy this all worked out. We are staying at Bay Lake Tower and I have an aversion to huge crowds - had the whole day planned as a non-park day and I would have been so disappointed if my dinner plans had fallen thru. (I did have a back-up ADR at Kona, and we would have gone to the TOTWL afterwards to see the fireworks. But I really had my heart set on CG!)