Great use of the Plant Journal

I would say it was moved into the sun too quickly and stayed exposed too long. I think it is stressed because of this and hence the curling. Leaves are strong due to turgidity as key cells are pumped with water. It is likely the full exposure reduced this turgidity

Here are some suggestions from Julian Sauls, an expert on Avocados

"Regular applications of a soluble houseplant-type fertilizer coupled with good light and watering as necessary will maintain the lustrous deep green foliage
characteristic of a healthy avocado plant. As with most houseplants, the avocado can be moved outdoors to shady locations during warm weather. Eventually the plant will become pot bound and should either be discarded, transplanted to a larger container or pruned back severely. "

http://university.uog.edu/cals/people...

It seems as if your might have had too much exposure.