Think about custom taxonomies as classifications a plugin provides, like e.g. “event categories” or “job types”. You can display them in an Ultimate Post List at each post assigned with them.
The label for custom taxonomies, displayed in the post list, was not editable. With version 5.1 of Ultimate Post List Pro you can change or delete the label to the term you like. The public name of the taxonomy was – and still is – the default.