The aloe mite only grows on aloes (and their close relatives). So unless you have acquired other aloes since you got this one, it most likely came to you already bearing the mite (but with no symptoms, or minimal). I have had aloes develop symptoms of mite infestation a year after being "cured" of aloe mite, with the only obvious explanation being that they somehow carried trace amounts of those microscopic animals for the whole time.
So I don't think soil moisture has anything to do with the problem. I don't think there is necessarily anything that you did to cause this. Some aloes are more mite-prone than others, but yours does not appear to be one of the more susceptible types. It is a very frustrating pest to deal with due to this long latency and the lack of easy chemical solutions.
I have dozens of aloes, all in the open air year round. A lot of the neighbors have aloes too, and I've seen mite infestations around the neighborhood. They often affect inflorescences, meaning there are big balls of mites waving around in the breeze and the mites are hitching rides with pollinators to other plants. So this will likely be a lifetime issue for me. I try to practice zero tolerance.
For you the situation is relatively simpler. If you clean up the area (bleach the pot, toss the soil, clean around where it was) and inspect your next acquisition carefully, there is a good chance you will never see mites again.
