Final vote for the location of the CIS-2017 tournament.

but they already created a separate thread about CIS-17
who made that decision?

CIS is a self-organizing project that has no direct connection to this resource. The target audience of CIS voted to hold it in Volgograd in 2017. The decision was made by those who regularly attend and participate. Check out the voting results.
Korolev's team (with the exception of Vigo) was offered a consensus: to hold CIS-2018 in the Moscow region.