Did you mean 1800 words? Most people will not learn 18000 distinct words during their lifetime.
I would guess, though, that the website was counting different forms of the 'same' word as distinct words - e.g., jump, jumped, jumping is three words rather than one word with several tenses. Obviously counting this way will multiply the same person's vocabulary several times vs the alternate way.
It gave me 36,800
I'm encouraged that there are more words for me to learn
[1] https://zwischenzugs.wordpress.com/2011/03/06/shakespeare_un...