Sorry, this isn't "suspicious": there is a publicly available court order[1] issued by the US District Court for the Central District of California for Apple to comply with, which you could have found in 15 seconds of Googling. This was not a FISA warrant or National Security Letter.
Just playing devil's advocate here (and I'm in no way full bottle on U.S. law) but from other posts here, one of the most contentious points about national security letters is the very strict gag order that is usually attached to them.
Yes, there's a publicly available court order. How would you know there isn't also an NSL?
[1] https://www.documentcloud.org/documents/2714001-SB-Shooter-O...