Sure, anything that can be sensed/known, can be studied.

It means that one cannot experience (look at, listen to, etc) a work and honestly say "I appreciate how this was human-made". There's no quality that can be imbued into a work that makes it discernable as made-by-human, as opposed to made-by-machine, or even made-by-nature (and eventually, maybe even made-by-alien). Not like one can discern and appreciate the lines and colours in a painting, or the tones and energy of a song. The maker of a work is extrinsic to it.