Here are some accompanying

I suspect that what you saw in November was normal leaf fall, including the leaf petioles, rather than 'branches'. A first year seedling is usually just a single stem, so nothing wrong there. Bark colour changing as it matures is also normal. Whether or not yours is still alive after the disturbance of repotting I can't tell from the pictures. But there is nothing you can do except water it judiciously and be patient and see if it leafs out. We don't know your location but walnuts are not the earliest of leafers

In northern Virginia/Washington DC area walnuts have not leafed out yet.

Ah sorry I forgot to mention, I'm in Atlanta, GA

Thank you both for the replies.

Walnuts have compound leaves that consist of a long, stiff stem and multiple leaf-like parts that branch off of the stem. It would be easy to think you had branches and simple stems. If you had some black root rot in a pot, you probably overwatered it.

I don't know how long you can keep a big tree like a walnut in a pot, but my butternut (white walnut) is pretty prolific about sprouting in my yard. Of course, the squirrels move the nuts all over the place.

If you have dreams of your tasty harvest, I've heard black walnuts are hard to shell. My huge 100-year-old butternut is very prolific. You have to pick up all the fruits before the worms get them, then getting the fruit off is a pain. The best way is a hammer. The fruits produce a staining dye, so wear old clothes. Smash the fruit with a hammer, pick off the remaining bits. It will take you several minutes per nut. Now, you have reduced 3-4 buckets to under one. Then, they need to dry. Putting them on top of a wood-burning stove is a good way to do it. After that, you need to crack the shells. Get our your hammer again. Be sure to have the nut on a very hard rock, otherwise, when you hit the nut with a hammer, the nut will make an impression on your board or make your soft rock crumble. Whacking hard enough to crack the shell, but keep the nut intact is hit or miss. It will take several minutes per nut. Then, you need a pick to extract the few minute bits of nut in each shell. Your bucket of shelled nuts has turned into a handful of nut crumbs and you have invested many hours to get to this point.

While the fruits can be used as a dye and walnut products are supposed to be good for skin, meaning you can make a yellow hair dye that will dye your gray hairs turning them into natural highlights, you need to process the fruits into dye immediately, as, once cut, the fruit flesh turns into a nasty, black, fly-infested, staining mush pretty quickly.

I personally would expect to see your black walnut further along. i would expect to see clear and obvious signs of life, like swelling buds, which i do not see. You are pretty far south and have had a very warm winter and spring. Perhaps it is late, but I am nervous for the little tree

Usually plants in pots need holes in the bottom …and to be raised …off the ground a little …to let excess water drain…and centering the planting will allow roots grow the same on all sides…