It would have to be, CS2 is the fourth major installment in the Counter-Strike franchise.

Then again, all kinds of companies take liberties with naming including numbers. Look at Windows 7 (12th major release), Windows 10 (successor to Windows 8), the game Battlefield 2 (third in the series), Battlefield 3 (three games after BF2), Battlefield 1 (after the release of BF4), etc.