Scanning through the abstract[1], it seems pretty likely to me that they did the actual screening in a lab, and it's merely that the fungus was originally from the rainforest. In fact, one of the 21 authors on the paper is from a Peruvian university, and he's likely the one who's group originally isolated the fungus.

[1] http://www.ncbi.nlm.nih.gov/pubmed/21764951