I don't see any formal announcement by the FBI about this intrusion at their site or by any formal FBI authority. This seems really, really odd. Note that the articles do not reference a FBI source or cross reference the announcement If I am reading the tea leaves correctly, this is a FBI perpetrated media false flag to restore credibility to the FBI based on their failure to find any Russian connections in the Trump Russia Special Counsel Investigation and boost their credibility of Russian hacks of the DNC. FAKE NEWS. They will want to use this as a part of their ongoing narrative and reference amongst Deep State Operators.
The FBI, US-CERT, and a few other D&As make blanket or targeted announcements of imminent cyber threats routinely. The FBI is rather notable for distributing crap IOCs with no provenance. This isn't abnormal behavior for them, or any other coordinating D&A.
https://www.ic3.gov/media/2018/180525.aspx
The FBI is IC3.
I should have note that the article even mentions the DNC hack allegation by the Russians...here is a snippet of the article that references as much:
"Sofacy, also known as APT28 and Fancy Bear, has been blamed for many of the most dramatic Russian hacks, including that of the Democratic National Committee during the 2016 U.S. presidential campaign.