No, it was the price hike of all eggs, not the difference between sizes that was the point. It never stood anything about that people would change to size 1 instead of size 0 because of the difference of 10 baht, as all eggs have gone up in price. That means the ones who buy size 0 will think that is expensive now as well as the ones who buy size 1. However, I am pretty sure they will also continue to buy the size they want as all gone up approx. the same percentage.
That will not change just because the egg seller fear something, that they have absolutely no evidence for whatsoever. What will be the result, is that you will have it harder to find the big eggs that you want, as they might stop selling them. However, don´t be sad. There is a great solution. Just take two and fry a double egg instead. Yummy! ????