I recently sold an IPhone 4 on the internet however the buy is saying he has a problem?

He bought the phone off ebay about a week ago, and received it the other day; however, he set me an email saying to access the iphone he needed my apple ID since it was still linked to the phone or I need to delete the device off my account which I don't know how to do, but I'm positive I restored the phone to factory settings erasing any details off the phone so I don't know how it handle this, when I've set up iPhones before I could enter my apple ID later in the process, its never being a requirement, and I don't see why it isn't giving him the option of logging in with an alternative ID, can someone tell me if hes trying to get my details or telling the truth- the card linked to my ID has expired anyway so he couldn't purchase anything, are there any other risks involved

All answers appreciated

You actually have to wipe it so your icloud ID is removed off it, thats a security feature, so you must not have done that. Don't EVER give out your icloud password.
I think you can actually wipe it remotely online by going to http://www.icloud.com/...icloud.com I know you can wipe it for sure (like if it was stolen, but someone would still need your password to set it up as their own, but see if there's also an option there to wipe the phone and also remove your icloud ID off the phone).