Taken in the context of your quote, historically speaking it would be referring to the generations which preceded Avraham.
As the Torah of Moshe relates, this is dealing primarily with the generation of Enosh and later, up to the the time of Avraham. That is also how Rambam recounts the development of idol worship in the Mishneh Torah, Hilchot Avodah Zarah v' Chukot HaGoyim, chapter 1, along with many other Torah sources like Sefer Brit Menucha and others.
According to archeological evidence from places like Çatalhöyük which is located in what today is modern Turkey, the worship of dust, meaning the dry earth on their feet, was a detail connected to the idol worship of an Earth-Mother goddess.
As explained in this link to Wikipedia discussing this subject, they focused on how the *Earth-Mother goddess*sustained life through her body, meaning the dirt and minerals.
In the context of how Rambam teaches the tradition, this would have started from a legitimate and permissible observation that G-d's presence is in all things and that part of His blessing comes to life on earth through the soil. But as generations became misled, rather than focusing on the true source, that all comes from the Creator, they focused their attention on the physical material things. In this case the dust of the earth.