As I understand it, US credit and debit cards are pretty much the same thing. So after a buyer has emptied his bank balance spending on his "debit" card, the card will switch over to being a "credit" card and allow him to keep spending until his credit limit is reached.
Many eBay merchants, usually those with brick and mortar businesses, have their own merchant accounts with credit card companies and can accept payments directly. Since these are electronically trackable, there should be no problem with spurious unpaid item disputes as there would be with cheque payments. However, if you were paying with a debit card, it would be difficult to get a refund because of the way they work, being essentially "e-cheques".
The claim that PP takes days to clear, is wrong and makes me suspicious. If you back your PP account only with your bank account, yes, that's true, you are in effect sending a cheque and it takes some time to clear the US and Canadian banking systems. However, it you attach a CREDIT card to your PP account, the seller is paid immediately.
Also you have an extra layer of protection in your credit card's Chargeback program.
Best to ask your seller what he means. This may be just a question of "two nations separated by a single language".