Needles fall off for a variety of reasons. Most grow new needles every 3 years. Shaded lower needles often don't get enough sun and fall. Mechanical injury can cause needles to drop..hail, mowers etc.There are diseases that cause needle drop. You seem to have researched this but I will add a website below. Dehydration can cause needle drop. The most important thing you can do is keep new trees watered until the ground freezes. You can wrap smaller trees with burlap to help prevent drastic temperature changes that cause problems but yours seems too big. Mulching to help keep the soil moisture is good. Just don't let the mulch touch the tree trunk. Keep the mulch back 12 inches to prevent dehydration by mulch. Although your tree has had several months to develop an good root system transplant shock could be a factor from initial planting. In general trees drop needles either because it's time to grow new ones or they are stressed by lack of water, nutrients or diseases. It would be good to wait and see what developes in the spring. My best guess from the picture is that this is normal needle regeneration. The websites give additional information. See: http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/choosing-landscape-evergreens/ And see: http://www3.extension.umn.edu/county/benton/county-horticulture-educator/article/preparing-trees-and-shrubs-winter For evergreen diseases see: https://www.extension.umn.edu/garden/yard-garden/trees-shrubs/spruce-tree-diseases/