I didn't follow up on the Reuters news piece from January titled "Exclusive: Apple dropped plan for encrypting backups after FBI complained - sources". Has it been confirmed? If yes, then your assertion is most probably correct.
That Reuter's piece is original reporting that Apple never responded to, so I would say that it's all but confirmed that they did in fact do this at the FBI's request.
https://www.reuters.com/article/us-apple-fbi-icloud-exclusiv...