OK.Am I seriously missing something here?Went to an auction...

OK.Am I seriously missing something here?
Went to an auction today in Melb S/E.The quoting range was 600-700.
Not many in attendance.
Auctioneer calls for opening bid.Young couple bid 605.Fine.But this is where I just don't get it and are happy to be proven to be stupid or ignorant on this one.
After no further bids the agent makes a vendor bid of 610k.OK.No other interested party.Original bidder bids again at 615 !? Agent makes another vendor bid at 620 and for all I know the original bidder followed up again after that.Don't know because I left shaking my head at that point.
My point is,why on earth would you bid against yourself?I repeat, at this point there was absolutely no other interested party or counter bids.
I know that the agent bangs on about the first right to negotiate blah blah blah but if there is no other interested party why would you bother.By doing this the bidder is weakening his/her bargaining position later because they have already shown what they are willing to pay up to.
Would they not have been in a better position to let the house get passed in at 610 Vendor bid rather than say 630 Vendor Bid?
What am I missing here?Please someone tell me.
This whole bidding against the vendor thing is absolutely insane.Imagine explaining this to a foreigner!Totally bizarre.