I have 0 (ZERO) doubts that the CIA, NSA and FBI already have backdoors into the Facebook (Facebook IS a CIA front operation afterall) encryption scheme.
They announce this to make the suckers think that they have privacy using the App.
I have zero doubts that probable cause is reqjuires for a warrant and probable cause requires evidence. So when they say "the content would also be inaccessible by the company, meaning agencies can’t get access even with a warrant." they are lying. They require evidence to get the warrant. Once they have the evidence and the warrant they can insert any number of spying programs on the target computer or just bust down his door. They do not need broken encryption or RNGs, although that is possible as well. But broken encryption is a boon for cyber criminals.