The reason I don't think it is a nutrient deficiency is because the pattern of the damage and the location in the middle of the plant is unusual. Deficiencies show up on either the youngest or the oldest leaves first and they cause yellowing or chlorosis. Sunburn would make the leaves look more red. Cold damage, I cannot tell you but camelias can handle a bit of cold. It doesn't like the wind though so you might want to protect it from that.
Nutritionally, camelias are acid loving so they do not need or want a lot of calcium. Magnesium is a micronutrient, you only need a little and the plant does not look like it has a magnesium deficiency. You have it in an air pot which provides good air circulation to the roots but you would have to worry about it getting adequate water in such a small pot especially exposed to drying winds.
Camelias are not fast growers but I would have put it in a larger pot myself with good drainage. I would not have used an air pot on a plant that was sickly to start with since I would want it to grow stronger roots.
I treat camelias like citrus and gardenias, they need regular feedings and I like citrus food. I use the vigoro brand it has low numbers and slow release nitrogen with micros. It also contains sulfur to keep the soil slightly acidic. Calcium is not going to be a major requirement for these plants since it will raise the pH and make the micronutrients less available. I fertilize in the spring with the new flush, after the blooms fade and have been deadheaded and if you live where it freezes, a couple of months before the hard frost so the growth has a chance to harden. Only a tablespoon for a pot that size is enough. If you want organic you can use 8-8-8 or 10-10-10 and I would put a tablespoon or so of sulfur in the pot each time. I don't care much for organic fertilizers alone for acid loving plants since they are not particularly rich in micronutrients and they are not acidic fertilizers. If you are on the coast how close are you to the ocean. Camellias really don't like salt air.