Well, don't know about this scase in particular
but i do know that situations like this happen
more often than what you think.

going for the 999 instead of the 001 is basically
the same in terms of money but it also depends of
the will of the person who places the bid.

The bid of 001 is placed with the will of
outbidding the previous bidder but trying to spend
the less as possible.

The bid of 999 is placed with the thought of "If
someone has placed a bid higher than this he/she
deserves the item more than me"

Personally i don't like either, also don't like
the random numbers. I prefer to stick to the
normal increments. I do this because this way is
easier to "hide" your bidding strategy from other
people, but that's another story....