Why did I get the coronavirus Economic Impact Payment?

I am filing a 1040 Form for 2019, but I have left the US last year, and I currently have no immigration status whatsoever (I am not, and was never, a citizen or a green card holder). I have an immigration petition with USCIS, however.

Why did I receive this money? Practically, for 2020 I should have no relation to the US: not a resident alien, and also not a non-resident alien. I do not have an address in the US, and I do not earn income in the US (at least in 2020 I didn't). I just have my US bank account, but nothing more.

Was receiving this stimulus a mistake? If yes, can/should I correct it?

If this was not a mistake, do I have to file taxes next year for the tax year 2020 to report those $1200 as income?