I wouldn't disparage that method of discovery at all. But some of the theories required to do it are:

- Many brute-force combinations of these specific organic molecules will yield interesting results (this is the main hypothesis of the experiment)

- We don't need to include the molecules that we haven't included

- We have good criteria for determining what results are interesting

- Our instruments/methods of phenotype prediction are well-understood and working as expected

Once the experiment is run, the observations are meaningless unless interpreted in the context of whatever prevailing theories the scientists have in mind.