Marcie's right, the tax records do show that this home has four bedrooms.
According to the San Diego County Web site, a bedroom is defined as "A habitable room totaling at least seventy (70) square feet in size, considered suitable for sleeping purposes, regardless of whether or not the room contains or has access to a closet and a full or 3/4 bathroom, and does nor directly open to a garage or other bedroom."
That being said, maybe the owner combined two smaller rooms to make one large room, and the records don't reflect that. In any case, the property is in escrow now.
If you'd like to see other homes like this one, let me know, I'll be happy to show you the interiors so you're comfortable making an offer.