You're right this is an effect of the Noisy/Quiet Mission and if I compare to the event hidden grotto pokemon I have it matches.
So I have to correct the underleved listing and catch all at level 15!
I'll try on white 2 later.
They're both generated by in-game mechanics, so there shouldn't be.
The only difference would have been where the game refers to for species ID, then uses the same generation subroutine.
edit: added W2 codes.
Between June 8th to June 9th 2019, Zekrom and Reshiram will be distributed at the site of the Korean League, the Seouliteum.
Source: https://pokemonkorea.co.kr/pkl2019_final