I don't know in this case because it was/is a secret mission and we probably will never know the whole truth ...
In this case we have a payload that apparently failed to cleanly separate from the payload adapter (according to a variety of sources). Both the payload and the payload adapter were made by Northrup Grumman, not SpaceX, and the two were mated together by Northrup Grumman, not SpaceX. Do you consider it "blame shifting" to point that out?
The fact that the second stage deorbited when and where it was supposed is just more evidence that the rocket performed as intended.