That usually requires a waiting list.
You just need to find out if he actually filed it. If he filed it, just contact that local housing authority and they will tell you exactly what they need. They will either have a form, or will want you to draft a letter stating you want him removed and why. The letter also needs to be notarized. I would also send it registered mail requiring a signature so you have proof they received it, just in case. You always want some sort of proof that it has been recorded.
It's just section 8 housing though. That POA would be for people who don't speak english, are illiterate, old or mentally ill. I know you aren't any of those and he was just trying to do you a favor, but just saying I wouldn't sweat it too hard. He's ultimately liable for the things he claims on the form.