I have a single small hard light brown growth on my camelia.

If this is where the flowers were then it is a seed pod. When it ripens and splits you will find some hard black if my memory serves me right pea sized seeds in it, if you are lucky. Sow, leave exposed to the weather and you may have a new Camellia in a fair number of years.

If the growth is where there have been flowers, then it may well be a seed case. If its somewhere that hasn't had a flower, it might be a camellia gall - usual procedure is to cut off the stem with the gall, if possible.