Seems like cross talking to me. They were responding to the erroneous claim of "input dimensonlity" being equivalent to data. What the first poster referred to as "internal data points" may be better described as the presumption of differentiability, that is, a small disturbance of the pixels should result in a "small" change of the labels. But it was ridiculous to claim somehow the total number of pixels is a meaningful measure of sample size. The pixels are not independent, as dramatized by the hash map example given above.