It sounds like the FBI has an website/email account set up like "I_AM_A_RUSSIAN_SPY@gmail.com". People email that account with offers of providing information

It sounds like the FBI has an website/email account set up like "I_AM_A_RUSSIAN_SPY@gmail.com". People email that account with offers of providing information to the russian government, and then the FBI goes and sees who had access to the documents which get sent over. In this case, only one person accessed all the documents, so even if he doesn't identify himself to I_AM_A_RUSSIAN_SPY@gmail.com, they still get him. It doesn't seem like this person was specifically targeted or had an operation against him. He just fell into the honey pot.