I'm still a bit of a novice when it comes to ebay

I've just been outbid on something, so I looked at the bids on the item and my username's displayed along with a few others but I've been outbid by Bidder 4 - but that's not their username, further down the list are Bidder 1, 2 and 3 also. Have they withheld their username? Is that possible?

I'm just curious