It operates at kernel level, it lives in the kernel, i would argue it “modifies” the kernel since it lives there. Also you cant say that its not a rootkit since there is no way to know what the anticheat does. If ea or riot games or others eant they can look at your files processes or just do whatever since they habe access to everything. This is a rootkit, you just hope they only look at the processes to stop cheaters but you cant know if they may send something back or execute other code.