Unfortunately, the job application asks if you were ever arrested for a felony. Doesn't matter that you may eventually win in court. The kid's right, the damage has already been done.
Damage has indeed been done, but not enough to derail his life. He will have to have an uploaded account of the whole charade to print out on every application. He could even use it as an opportunity to engage at a personal level. Most people are coming to loathe the existing police state mentality. There might even be a malicious prosecution case in there, although those are -hard- to make stick (by design).
IMO, just as in testimony, the question should be: “Have you ever been -convicted- of a felony? If so, explain in detail.”
People need to look closely, and listen attentively to who they consider for the high and dangerous office of prosecutor. It is a complex and difficult task, and is not for those whose solution is to cruise on autopilot.