I am suspicious because he said mounds, red ants don't make mounds particularly, over time the gravel and debris build up but not to the point of being called a mound. Red ant holes are usually a large flat area cleared of vegetation with distinct paths radiating outward.
Red ants are not outwardly bothersome unless provoked to a greater degree than it takes fire ants.
Red ant bites are quite painful.
Red ants will fight with red ants from other colonies, therefore, others colonies should be a significant distance away. It could be possible that its a very old colony with multiple entrances.
Fire ants mound up quickly, overnight, and are steep. They can have several in one area and can be spotted from considerable distance. The mounds are unstable and resemble finely ground coffee at times.
Fire ants will attack with very little provocation. While individual bites are not as painful, they attack in force and the multiple bites can make you ill an cause death in the weak. The bites form ous filled blisters.