The post actually has a lot of small grammatical errors typical of someone not so fluent in English:
>> My reasoning went as follow: // My reasoning went as follows.
>> Is there any other numbers where this happens? // Are there any other numbers
>> I didn’t had paper at hand // I didn't have (any) paper on hand.
I'm not here to proofread a fun blog post but it's far from incredibly well-written English.
> that requires incredibly deep knowledge of the type system.
I think the solution needed more clever maths than deep knowledge of the type system---the type system knowledge can be self-studied from documentation. The clever maths, one can get used to if you Leetcode properly (you don't even need Leetcode Hard to get exposure to that).
If anything doesn't track in this respect, it's the claim that author doesn't have any kind of formal education. Not even high school? That will be extremely impressive. But maybe something got lost in translation there, or just careless exaggeration.
> Here's a viral calling card that would almost guarantee countless interviews (including from my company!) and they aren't capitalizing on it.
>> I don’t have anything to sell just yet, I am not a tech influencer so all you got was this post about a somewhat challenging FizzBuzz.
Yeah, not everyone is out to sell something, not every blog post is written as an opportunity to self-promote.
The story is definitely rather strange, even without taking into account the language barrier and the general absurdity of most tech interviews, but it's not outside the realm of possibility.