I don't really care what the FBI says, given that the FBI is a group of Democrat Party thugs and enforcers. While the areas around Portland appear relatively sane, there's no way you can trust the official lines of communication if they are at all connected to Portland or the Oregon governor's office.
Rioters are willing to block cops inside a building and set it on fire, so why would the fire-setting criminals of antifa and BLM hesitate to burn down the lives of people they consider to be fascists?
Given that any condemnation of Antifa seems to bring unholy retribution, why should we trust the official narrative? If people say that they're seeing Antifa setting fires, then my response would be make sure you adjust for elevation before you pull the trigger.