no it doesn't mean that. if no model was generated by DBE, it means that there were not enough valid samples placed on the image. you can place 1000 samples but if the tolerance is set too low for the particular image, no sample will "capture" enough of the data underneath the sample, and DBE will reject that sample... it's as though it was never placed.
DBE or ABE can never know what is a gradient and what is signal; for instance if you place a DBE sample too close to the halo of a star, DBE will interpret the halo as gradient and darken the result image there... but that is a mistake; the star halo is not an LP gradient, it is just a dim feature that seems like it might be a gradient to the tool.
rob