It sounds like the appeal was shit-flinging against the whole process and something stuck.

...In his appeal, Smollett argued that Cook County prosecutors dropping the case resolved it, similar to a deferred prosecution agreement, particularly because he forfeited his bail.
Attorneys for the state, though, among other arguments, contended that prosecutors who drop charges are not precluded from refiling charges in the same case.
In the majority opinion delivered by Judge David Navarro and concurred with by Judge Mary Ellen Coghlan, the judges wrote that Smollett “challenges virtually every aspect of the second prosecution that resulted in his convictions and sentence.”
“The record does not establish that Smollett entered into a nonprosecution agreement with the (Cook County State’s Attorney’s Office), in which the (office) agreed to forgo further prosecution of him in exchange for his performance of community service and the forfeiture of his bond,” the opinion reads.
[earlier in the article] After the decision, Smollett asked the state’s high court to hear the case, a decision up to the discretion of the judges. In asking the court to review his case, Smollett had argued that the lower court’s opinion “threatens to upend all informal and formal deferred prosecution agreements."