question about Terms used for TI report

Agent asked me yesterday about a thermal inspection that was done for her son in Florida. Her ? was about the wording the inspector used. He told her that a wall behind the tub showed a higher density than the other walls and so this meant it was full of water. I am not a thermal imager but I always thought that it measured "thermal" properties, not mass density properties.
They tore open the wall, found a small section to seal up, but to do it had to remove the shower drain pan. Whole lot of work, but no where near what the image was supposedly showing.
So, is the term density used in TI inspections or is it thermal imaging? Thanks