Definitely think it's a troll.
But on ebay you can end up bidding multiple times in a row.
If you enter a bid, ebay puts the lowest bid that works. So for instance if the current bid is $100 and you enter $500, ebay will put "$101" or something as your bid. If someone else comes along and bids $300, ebay will automatically bump yours to $301 and tell them that they didn't bid high enough. So it looks like you bid $101 and $301 right in a row, but someone else bid and yours just automatically trumped theirs. Basically you go in and say "I want this. The most I'll pay is $1,000." And ebay keeps bidding for you until it reaches $1,000 and then notifies you that you are no longer the highest bidder. So in the end it looks on the screen like you outbid yourself several times, when you were actually just outbidding someone else automatically.
All that being said, I think it's probably just people who think they are funny.
Side story: I accidentally bid $10,000 on some concert tickets once because I was trying to type $100.00 and missed the decimal! Thank god I only ended up paying $150 because the bidding didn't get very high, but I wasn't sure what I was going to do if it got much higher! I guess I would have had to email the seller...?