I’m not familiar with this type of tree specifically, but bringing trees indoor (even with grow lights) can cause foliage drooping and even death. After the tree adjusts to being inside it might rebound.
Beyond light differences, indoors is usually very dry in the winter and could also be causing issues. Misting and raising the local humidity might help too.
Hi Gregory, where did the nursery owner keep it? Syzgium can’t tolerate temperature changes or draughts of any sort. Although you didn’t do any root work were they compacted? It may be that it isn’t getting sufficient water if they were.