He should be upset that it wasn't possible to be fully exonerated, not proven was the best possible outcome for him. If he didn't say anything racist then I would imagine that he is still very upset.
Milan Baros made the same gesture, but didn't say anything, in 2007, to Stéphane MBia. After a similar process to the Bong/Rodriguez incident, Baros was ruled innocent of racist behaviour but banned for the gesture which was deemed ungentlemanly. There is a history surrounding this gesture being aimed at African players. Whether Rodriguez said anything racist or not, it doesn't mean that there wasn't something wrong about his actions, he probably wouldn't have even thought of doing it to an English player.
For the record, I'm not calling Rodriguez a racist, I think he (regardless of words said), like Baros, made a stupid decision to try and rile up an opponent in the heat of the moment during a competitive game without thinking of the consequences. He made a gesture that is historically linked with racism (just look at soap adverts over the past 150 years) and has appeared to regret it. It should now be left in the past, but to pretend as if (because he didn't pair words with his actions) there isn't any racist motivation (subconsciously in my opinion) involved is being blind to the wider issue.