Morrill goes on to say, “Character in nonfiction is shaped as much by an author’s omissions as by action.” You might change that to say, “Character is shown or shaped as much by implication as by action.”
BUT there are other dimensions that we must think about that may require more time to choose how to show. We are now thinking of the dimension that we think of as within or insides or the depth of a person. Though these things may be more internal or foundational, they are as important or perhaps more important.
Remember. whether you are writing fiction or nonfiction, you must know who you are talking/writing about. So think about what you know and what you must discover.
Do you choose to make your point by developing one issue ata a time or do you put lots of "nuts" in there and let your reader sort them out? I am not sure readers like guessing.