FB has more information about other channels than you do, I.e. for all you know they have algorithms favoring users to see FB ads that are on path that usually leads to your site based on FB pixel tracking. Then all the multi-attribution ROI of FB is nonsenses but you have no idea.

I'm not saying they are doing that, I am saying be especially careful with anyone in advertising who is misleading and who doesn't try to protect their reputation by being exact in what they say.