Ok, but let's acknowledge the difference between no data (depicted as no colored cell in the map) and data which reports high interference (depicted as a red cell). In remote western Aus we see a few red cells to the west of a large area of empty cells. So they do have ADS-B receivers there, and at least some of them are reporting a troublesome NIC, and there are enough reports for FR24 to place a colored cell there rather than an empty cell. Why exactly do you think that a red cell comes from no data or very limited data, when the article does not indicate that no data / limited data results in a red cell?

"No data" cells are grey on that map, but western Australia has a couple of red ("high interference") cells.