Lot of nitpicking from their side and the fact that they require you to implement a "simple" task of this size and magnitude in your own spare time, unpaid. Red flag should have been there right away, you could have said "thanks" and move on (because there's still a pretty huge dev shortage in the market so half a dozen others in place of them).
And don't get met started about the rockstar and ninja crap that companies/teams are throwing around, and the silly coding tests where they required you to have memorized every obscure detail of a language's syntax or of a framework's API.
You know what you're worth, if a potential employee doesn't get it, then JUST MOVE ON.
We're a place where coders share, stay up-to-date and grow their careers.
We strive for transparency and don't collect excess data.