Part of "mutual annihilation" during the cold war was that every nation knew full scale invasions and annexation were a thing of the past. Both nations knew full well if their hegemony was at stake, they would launch their nuclear weapons at a minimum of self preservation, at a maximum of causing severe attritional losses to the victor. Which is why the nations on the offensive tend to not want the other nation backed into a corner. So it's a weird game of war chess where you want them at a point where the know something like that is the only way out but they can still negotiate and save face.
I have not read the paper the video is referencing. But, I assume all major military papers would discuss the biological weapons to a certain extent. Actually implementing is the scary part