Q.does the description “stem cutting” really mean the stem of the seedling from which a length is taken, and not a recent branch?
for a Fall season rooting attempt, should the attempt be done indoors so that leaf-out will occur in the warmer temps?

Certified GKH Gardening Expert
No, a cutting will be from an axial stem. The stem of a seedling is way too young to take a cutting, as they don't have branches to take cuttings from. Cutting the main stem of a seedling will be met with the plant's quick death.
When you take a cutting, make sure that this is from a mature specimen, or at least from one that has grown enough to recover from cutting in half. It needs to have branch or leaf nodes to replace what you have cut from the top. It is best, however, to take a cutting from a branch of an existing tree, so that you know you won't be hurting it by taking such a small amount of the tree.
This article will help you to take a cutting:https://www.gardeningknowhow.com/ornamental/trees/tgen/how-to-root-cuttings-from-various-shrubs-bushes-and-trees.htm