As it turns out, there is no issue at all.
California state athletic commission executive officer George Dodd told MMA Fighting that Castillo was never invited to a meeting, and that he faces no review.
"There's no letter and there's no hearing," Dodd said.
The 12-4 lightweight returned to the win column with a first-round TKO over Shamar Bailey at the event. Afterward, he celebrated with a muted dance but UFC cameras cut away moments later. Allegedly, however, what he had done off camera was enough to warrant a possible penalty at the hands of the state commission.
Castillo did not respond to a request for comment, but Dodd said he had spoken with Castillo and informed him he was never under any review and had acted within commission rules. Dodd said it was his understanding that Castillo's teammates had played a prank on him. Castillo has since deleted the tweet from his timeline.