The criterion is distinguishing words from non-words. That's it. You don't have to know the meaning. You just have to distinguish it from a word-like series of letters. If you incorrectly identify a non-word as a word, your score is penalized in some way.

I was surprised to find Bolshevik in the list of little known words. I learned about it in secondary school during classes on Russia history (live in France) and everyone is supposed to know his Lenin from its Trotsky. Although we spell it « Bolchéviques ».

I was surprised it was on the list, but for the opposite reason. The others could be excused as technical or niche vocabulary, but bolshevism was critical to the third-most influential (for English speakers) historical event of the 20th century.

They know it as a 1950s slur for a Communist, not as opposed to Menshevik (which triggers my spellcheck btw.)

Of course we do comrade.