Is it right for John Oakhurst to keep secrets from the young couple, such as why the outcasts have left Poker Flat, or what has really happened to the horse?
It is certainly in character for the gambler, John Oakhurst, to be reticent about revealing what he considers only the most necessary information. So, in this sense, it is "right" as then the story retains its verisimilitude. When Piney Woods and Tom Simon arrive, Oakhurst recognizes Tom as the "devoted slave" whom he acquired after returning to the young man the money lost to him in Sandy Bar with the exhortation to not try to gamble again. Now, if he informs Tom that he has been run out of Poker Flat, "the Innocent" might try to restore the gambler's good name by riding to the town and testifying about Oakhurst's honorable character. So, in order to prevent the young man from being harmed by going to Poker Flat where his testimony would be a futile effort, the gambler does keeps secret his banishment from the town.
For possibly much the same reason, Oakhurst does not inform Tom that Uncle Billy has stolen the provisions and the mules and horses. For, if Tom knows who is the culprit, again, he may try to find him and recapture the stolen horses and some of the provisions. In this effort, Tom may easily be slain, Oakhurst knows; therefore, he remains taciturn about Uncle Billy's nefarious act.
There is a third reason which certainly enters into the gambler's decision to remain quiet on these matters. For, when he warns the Duchess and Mother Shipton about Billy's "defection," he says to them,
"They'll find out the truth about us all when they find out anything," he added, significantly, "and there's no good frightening them now."
Young Piney, who is only fifteen, may easily be frightened to think that her female companions are a "scarlet" pair of women, and Tom, "the Innocent," may be terribly dismayed to think that the gambler and Billy are outlaws. Indeed, he may be worried that harm will come to his young love, as well as to himself, especially from Uncle Billy.