What is the most likely reason that oakhurst believed the citizens of poker flat were after him?

The most likely reason that John Oakhurst believed the citizens of Poker Flat were after him is because he was a known gambler and the community had decided to expel certain "undesirable" elements. In the story "The Outcasts of Poker Flat" by Bret Harte, the town of Poker Flat decides to rid itself of certain individuals who are viewed as immoral or problematic. Oakhurst, being a successful and unrepentant gambler, would have been naturally seen as a target for this sort of moral cleansing, especially since his craft was often associated with vice and unproductive behaviors that the town's more upstanding citizens sought to eliminate.

Given the context of the story and the time period in which it is set, gambling was often seen as dishonorable and a vice that could lead individuals down a path of ruin, both financially and morally. Oakhurst, being an extremely successful gambler, likely understood that his lifestyle was at odds with the evolving social mores of the community, and that the recent vigilantism exhibited by the town's people was a direct threat to him.