Bruce Schneier has said something similar, having seen some of the guardian documents. https://www.schneier.com/blog/archives/2013/09/the_nsas_cryp...
EDIT: Ah, it appears to be confirmed at http://www.huffingtonpost.com/2013/06/10/edward-snowden-glen... ... Thanks!
Second paragraph into the article describes Snowden's requirement to use PGP while contacting Greenwald at the least (although it's a tertiary source and very sparse in technical details).
It's not enough to merely tell people "install PGP." Snowden presumably went into meticulous detail about precisely how to be completely secure. Even something small like "here is the exact exe installer to download" is probably significant, because that would mean that specific installer is clean and free of NSA tampering.