Yes, you're making sense and no, that's not terribly unusual. As 'whateve' pointed out, many bidders wait until the last minute and then bid frantically trying to win.
I once bid $100 on an item with a 'fair' price of maybe $50 (but I really wanted it). I was 'winning' at $20. Then, about 12 hours before the auction ended, someone bid $30. I was still winning. Then they bid $40. I was still winning. Then they bid $1,000. Now they were winning at $102.50 (since my high bid was $100).
Ok, fine - they really, REALLY wanted it. I was ready to let it go.
An hour before auction end, they cancelled their $1000 bid (making mine the high bid again at just over $40). Then they bid $99 - making me the 'winner' at $100. Now THAT'S shill bidding. I complained to ebay - they did nothing - so I ended up paying $100. This happened years ago - rules might have changed a bit since then - but it still bothers me. Not the $100 - I was willing to pay that - but the fact that the seller got away with it.