Appears to be a mistake, but needs gorhill to appeal to make the reviewer aware of the mistake and to be able to fix it, which he doesn’t feel like doing because he thinks it’s unlikely to have been a mistake.
Update: now reversed, but gorhill removed it himself just to not have to deal with the review process and the possibility of human error anymore.
I imagine part of the reason is that uBOL’s target audience might have less of a problem with not getting it via AMO? After all, it probably wouldn’t even exist if Chrome didn’t pull its MV3 shenanigans.