??
i think the point is that "islamism" refers to a political ideology
derived from a religion. obviously islam itself is not a political ideology, it's a religion, but because a large number of people follow the religion, there are political ideologies or public policy derived from it. the same, of course, can be said for christianity
ie, believing in a religion like christianity, buddhism, islam, etc. isn't the same as believing in a political ideology like communism, capitalism, libertarianism, etc. even if the former may inevitably influence the latter
maybe if you consider all religions 'ideologies' then it works, but the term 'ideology' generally connotes something political/economic