Such a war might not necessarily be limited to Europe though, as the various alliances are spread globally, and thus the designation "World War" would again be appropriate. Anyways, my point was more that such a war would be much more unlikely with the Soviets as the hegemon across most of Europe. This doesn't preclude proxy wars from time to time of course.
If your history only diverges around the bombings of Hiroshima and Nagasaki, it's hard for me to imagine a likely scenario where the conquest of Western Europe (minus UK?) by the USSR wouldn't qualify as "WW3". (Maybe if it immediately follows WW2 - for which I somewhat doubt the Soviets has the strength for, considering the heavy US presence... and even then this seems like hair-splitting ?)
It really depends on whether the conflict stays restricted to Europe or not. A regional war is not a world war, even though Europeans might regard themselves as the navel of the world. As you say, a hair-splitting exercise for future archeologists (might actually be cockroaches or aliens) studying the leftovers of human culture.
