As in summary: When the armor stand inventory item is given a custom name in an anvil, that custom name is not copied to the armor stand entity created when the item is placed. This behaviour is different from other items that create entities when placed (i.e. spawn eggs) which do copy their custom name to the created entity. This functionality would be useful for map makers/datapack creators.

Reproduction steps:

1. Give yourself an anvil, armor stand and spawn egg (any mob)
2. Give the armor stand and the spawn egg a custom name using the anvil
3. Use the spawn egg; observe that the created entity has a custom name
4. Place the armor stand; notice that it does not have a custom name