If it is a reserve price auction Ebay will automatically raise the bid to the reserve price if the maximum bid exceeds the reserve price. 3750 was almost certainly the reserve price for the auction.
Alternately Ebay also raises the price automatically above the lext lowest bidders max bid price. So if Bidder6 had placed a max bid of 3740, the next max bid in excess of that would have been raised to 3750.
The seller has indicated that if the payment is less than the reserve price he may cancel the auction and not sell.
When the max bid was placed in excess of the reserve price the buyer has indicated to Ebay that he is willing to pay as much as that price on the auction. Ebay raises the bid level to that minimum number so the auction can be completed. Until the reserve price is met, the auction increments as normal.
If your friend had won the bid at 2510 and that did not meet the reserve price the seller would most likely walk away and relist the item and hope for more money next time.
For instance assuming the reserve was 3750:
1. Your friend bid 3745, the bidding would have ended at 2510, and nobody would have won.
2. Your friend bid 5000, he would have won at 3750, and gotten the item.
When reserve price auctions end below the reserve price, if you are the winning bidder it can help to follow up with the seller to check on their position. If the item has been relisted, a couple of times, and you got close to the reserve, getting an email from you might convince them that their expectations are a little to high, and finish the deal.
Auction hint: never place a max bid more than you are willing to pay, especially in a reserve auction.
Auction hint number two: Figure out what you want to pay, and add a couple of padding dollars you are willing to part with so you don't just miss.
Shlep