This is the reason he thinks computers won't be creatives. But testing theories in science or math can be automated(in most cases). So technological creativity is possible ,and that what's the singularity talks about(although the testing can be quite lengthy and expensive ,which might really slow the singularity maybe to the point of no singularity at all).
And as for artistic creativity - that depends on if we can build some model on how humans evaluate art in general. Who knows, maybe we can build a good model of that. We've certainly improved from say 100-200 years ago where most artists we're considered geniuses, to today ,where a large percent of commercial art is at least is generated or least guided by knowledge on how to create good stories, etc.