I got that on a couple of mine from the first freeze we had back in November. The temperature had not been below freezing here yet at that point. Then, this front comes through and drops our temperature below freezing for the first time. It dropped the temperature, not to 30, or even 25, but 19 degrees. I believe the resulting damage could be attributed to the fact that the plants had not hardened off at that time.
Don't worry about the camellia leaf damage, the new growth will come out in late April and early May and all will look good again.