Yes, that is partially true. Here is the actual verbiage from the eBay site...
"Cookies have two distinct expiration dates correlating with our "Winning Bid" and ACRU tiers.
"Winning Bids": Cookies expire 7 days after the cookie is placed. During this period of time "Winning Bids" will be compensated according to our pricing structure.
ACRUs: Cookies expire 30 days after the cookie is placed. In this period of time a user must become a confirmed registered user and place a bid or use BIN to purchase an item on eBay."
ACRU's = your $25 for a new eBay member sign-up. People who visit your site and click on your eBay link are tracked for 30 days. If they join eBay within that 30-day period, you make $25.
Winning Bid = If they buy anything else on eBay, you make a commission for 7 days.