Of course, the colonizers were ethnocentric... as stated above, it is human nature for all people to be ethnocentric... it is part of what makes a group "gel" together... all societies are ethnocentric, they all believe that their way of doing things is the right way; otherwise they wouldn't be doing them that way.  The treatment of the native people by the Europeans is really nothing new either.  There has seldom been an invading group that has not forced their ways upon the native people in world history.

The European colonizers were indeed ethnocentric, for the reasons cited above. It is interesting, however, that for many intellectuals in Europe, contact with people in the New World was cause to reconsider some of what they had believed about their own way of life, and even to begin to challenge the notion of ethnocentrism itself. There are many manifestations of this, including the "noble savage" trope that appears in literature and philosophy, but some thinkers from Montaigne to Diderot took it even further, arriving at conclusions that we would recognize today as cultural relativism. These were, of course, not the views of the actual colonizers themselves, though especially in the American South, many individuals adopted native ways of life, including marrying Indian women, for diplomatic and trading purposes.

It is human to be ethnocentric, and it takes hard work to not be so, work I believe it is necessary to do.  The colonial powers were clearly ethnocentric in their presumptions that the land and people were theirs for the taking, in making no attempt to learn about the culture and people they were colonizing, and in their disregard for human life in their colonies.  I would go so far as to say that not only were they ethnocentric, but they were also dehumanizing.  Colonialism is nothing more than slavery, and those who enslave always dehumanize the enslaved. 

It's hard to imagine arguing that the Europeans were not ethnocentric.  The very fact that they felt that it was appropriate to come in and colonize another group of people shows that they felt superior.  The fact that they talked of their "civilizing mission" shows that they felt they were ethnically superior as well.