***** NOT A TEACHER *****
As a moderator, Beeesneees has the duty to make sure that learners who come to this website speak the most current and natural English.
So she wants to make sure that learners use an article in such a sentence. Since the context is missing, it is impossible to know whether it should be “a” or “the.”
When I first read that sentence , I, too, was slightly taken aback, but the more I read it, the more I liked the sound of “He was incidentally news dealer.”
I checked up on the author, T.B. Alrich (1836 - 1907). He was an American novelist, poet, travel writer, and editor (according to Wikipedia).
I think that established writers are often able to break rules. Furthermore, he was writing at an earlier time.
My books tell me that sometimes the article is optional if the noun refers to a unique role. Thus, we can say:
John F. Kennedy was (the) President in 1961. (That is a unique role, for there was only one president in 1961.)
There is no context for the book’s sentence. But it is possible that there was only one “news dealer” in that place, and “he” was it.
Learners, of course, should always follow Beeesneees’s advice.
As they become more fluent, they will discover that there are always exceptions to every rule.
James