The particular history of Turkish civil-military relations is something you should read into, because it's incredibly interesting. The military has historically been the guard of the official state ideology, ie Ataturk-ism, which is secular, nationalist, and in opposition to Islamic rule. If you think the greatest threat to democracy is theocratic Islamic rule, and that Erdogan's broadly Islamic (though democratically elected) government is likely to lead to that, then yes, it makes total sense to talk about the Army as the guarantor of democracy.