Yes, I also think the “built in” targets in LingQ are much lower than the real level. Although I got 20000 words (including many specific terms, Japanese words) in French, there still are many basic words (including verbs’ conjugations). I always find out such words are blue-highlighted even in beginner one texts.
In conclusion, each one has each domain. Some one is musician mathematician, business man, etc. So he or she is more familiar with certain terms than others. Counting level is, in my opinion, a certain indicator to motivate learners, but is not perfect one.