This is a For Sale By Owner listing and you are correct. The owner only posted pictures of the outside - not the inside of the house. Owners and realtors make the decision of how many pictures to post to their listing. Websites like Zillow and Trulia have no control over the listing and cannot add or delete photos.
If I were you, I would contact the owner and visit the home. You have the advantage to negotiate. The owner failed to upload any photos which means buyers are not going to be interested. Time for you to negotiate a lower price. Without photos, this home will sit on the market for a long time.