You can also check the appraisal district that the house falls in and do an address search to find out the history on the property. Most county's have the capability to show the transaction history on the property EVEN if it did not sell through a Realtor.
Hope this helps.
Kathy made a good point about some listings on Trulia being manually added, but generallly HAR will be the most accurate site. I would guess as well that the possibly re-listed. Possibly an investor bought it or it was a short sale at the time and the bank took over? The possible situations are endless.
Without knowing the address it would be difficult to say.
Sorry we can't be anymore specific, good luck.