Sounds like the buyer changed his mind and decided that was his only way to back out, rather than contacting you.
Based on the date of the dispute vs the purchase date, I don't see how he could win any dispute.
It is normal for Paypal to take the money out of your account during any dispute.
If it were me I would call Paypal so they know what's up.
You say you sent him an email asking him, but you will also have to converse with him through paypal, then paypal will make a decision.
I figure you're not worried about the money, and would have reimbursed him, had he been honest about it, and said he had buyers remorse.
There's always the chance he hit the wrong button I guess.
It will be interesting to hear what the guys excuse is.