It's still an insane feat, since it typically takes actual language learners years to get anywhere close to a native speaker's inventory of 10,000+ words.
But Nigel Richards? He's on another level: https://youtu.be/35rqRFXPWJo?t=143 knowing even exceptions to patterns and differences between dictionaries, for 9-letter words, in a game where players only have 7 letter-tiles.
https://isaak.net/mandarin/ is an example
edit: Isaak is great, but it was 22 words per day not 50
The claim here is memorizing a full dictionary in 9 weeks. That has to be at least 40,000 words in 63 days. 634 words per day. And then or forgetting it.
It's beyond rare. Its alien.
In school 35 words a day would be really pushing it for me. It had a really hard time learning English words. I had to study like an hour for 20 words to pass the test. But I learned grammar really fast.
I start by front loading all the grammar study up to upper-intermediate level as fast as possible. Usually a premade Anki deck of a few thousand sentences will be available for this.
Vocab I pick up from native media. I just read or watch whatever I'm interested in, lookup words as I go and put them into Anki. I do full immersion and it works well as access to entertainment in my target languages is a key goal.
Pronunciation I pick up through a crap tonne of exposure to native media.
Conversation is through a combination of private tutoring and finding people who speak my target languages to hang out with.
If you don't actually know the meanings of the words, they may as well be random. What do you have to remember them by if you have no meaning to attach to them?
It's not even an insane feat. It's inhuman.
Also if one takes character patterns (which words are) and attach other characteristics, such as number of occurrences of individual characters or use ascii numbering to convert to numbers, then these character patterns (aka words) might be simpler to memorise.
Meaning is only necessary if you intend to speak the language.
If you're applying mnemonics to remember things then the act of doing so also takes time and energy. The issue here is the volume of information in the stated time span.
Just a pity that there are so many regular humans.
Also Nigel Richards probably doesn’t spend much time watching Netflix or shopping on Amazon. Probably very much focussed on scrambling.
A world where one in eight billion binge watches Netflix would truly be an interesting world!