No. Most liberal arts majors either doubled in a "harder" field, or minored in Education/Business/etc. as a back-up option. The Edu and Business major and minor required a CS course. So most of the liberal arts students ended up either minoring in a STEM field or else taking CS1.
If anything I would assume the opposite of a selection effect.
I, personally, double majored in philosophy and computer science. I think the upper level CS classes would have washed out most of the philosophers, but I agree that the intro classes were fairly accessible.
If anything I would assume the opposite of a selection effect.