I accept the story as it was reported. I haven't seen anything that would cause me to doubt anything about it. Let's run through it quickly.
Bubba Wallace's team discovered a noose hanging in their assigned garage so they reported it. That was exactly the right thing to do, given recent events such as Bubba Wallace taking the lead on asking NASCAR to ban all use of the Confederate flag and the many death threats that he received as a result. The noose is frequently used as a death threat to blacks. Good, so far?
Next, the FBI investigated and confirmed that it was indeed tied as a noose, but they determined that the noose had been there for quite awhile and therefore wasn't specifically targeted to Bubba Wallace. Whoever tied it wouldn't have known that Bubba Wallace would be assigned to that garage a number of months later. The media reported all of that, as it became available/known.
That should have been the end of it, but now there's some weird sick backlash against Bubba Wallace for reporting it in the first place. I don't get that part at all. He did exactly the right thing in reporting it, just as he did exactly the right thing in asking NASCAR to ban the use of the Confederate flag.