I took a look at my school's match list and noticed there were about 5 people listed with only medicine or surgery prelim's without an attached specialty. I'm guessing it means they had to SOAP in?
It probably means they scrambled for the spot, but there could be random exceptions (i.e. couples matching and went low on the list to ensure would stay in city of choice with spouse, matched into a prelim spot but not an advanced position, etc.).