and they were the ones who asked the FBI to come in, I'm guessing they must have thought it was a threatening gesture too. So it's not like Wallace or his team called the FBI to have them look at it.
And even if it was hanging, I could see why they thought it was a noose meant to intimidate. Look at the left garage in this picture:
https://pbs.twimg.com/media/EbLWXUfWsAAejh6?format=jpg&name=large
and then noose from last October:
https://imgur.com/a/FvRsI3k
That's clearly a noose while the other door is just a loose rope. That combined with what Wallace has been saying, I'd definitely think that noose was tied and left there for Wallace without proof otherwise.