I think the word "spontaneous" best captures this phenomenon. It is an indication that you are conditioning yourself to be more critical of reality. Regardless of which technique you use, you will likely have these spontaneous lucids mixed in with others.

Delving deeper, consider how you are doing reality checks. The MILD approach is to identify dreamsigns that appear in your past dreams and in real life. When you encounter a dreamsign in real life (say, your dog), you perform a reality check. Using this method, the moment you become lucid will be more deliberate and obvious (see your dog, perform reality check, fails, "I must be dreaming!"). This is prospective memory in action.

But there are other approaches to reality checks. If you use a timer reminder or do an RC just whenever it comes to mind, you'll likely get more of the spontaneous lucid moments. If you practice doing an RC any time you see something strange (but not necessarily a pre-selected dreamsign) then you'll get something in between.