If there is water staining on the wall nearby, there could be your source for the water on the flooring.
We find water stains on walls are usually caused from some type of leakage at the roof. Most common is leakage around the sewer vent pipes.
Was there a laundry room near this area, a bathroom where a toilet or tub could have over-flowed. The possibilites are many.
The idea of it coming from below as someone else said sounds bogus.
Remember, an agent most likely will tell you anything to sell a place. Never bank on their information but base your findings on your inspection. Use the force.
