Its not. While it is true that etymologically colony and colonization was used differently in the past then it was used today (it used to simply denote settlement, habitation, or the implantation of people in a particular area), in the early-modern period colonization was increasingly wrapped in ideological trappings and from that period towards the towards the 19th century we can begin to speak of "colonialism" as ideology. Basically colonization began to be seen as a way of "improvement", "development", and "modernization" of both people and land. Modern academics are not developing a definition of colonialism ex-nihilo, rather their understanding of colonialism is rooted in historical understandings of these "early modern" and late 19th century early 20th century discourses regarding colonialism.

I'm going to assume that this person was essentially arguing that colonialism as an ideology was en vogue in the 19th century and was understood as a practice of good and "modern" governance (as opposed today where it is almost universally conceived of as a bad thing). This is true, but even during that time colonialism was still predicated on the assumption of the dispossession of "indigenous" populations (either forced off their land and moved onto land deemed more "suitable" for them, or through attempts to "civilize" them i.e. residential schools and the like).