When Faceit doesnt require you to download their client/AC then you play on the server sided AC.
If you have Faceit premium/supporter you MUST have the client/AC installed inorder to play or queue.
SourceMod Anti-Cheat is a server-side plugin comprised of different modules to help protect your gameserver against common threats, hacks, scripts, exploits, commands, cvars, or cheats currently being used today to cause your servers harm.
Information on the various parts of SMAC can be found in this wiki.