That still doesn't mean that citizenship automatically makes someone nationalist, which is what was being suggested. One can be a citizen without being a nationalist in terms of values. The concept of national pride is a completely made up concept to excuse all kinds of racist horrors.
You are focusing on only the most radical characteristics of nationalism. Were there no national pride, it is unlikely that independent states would exist entirely. For the most part, any identification with one segment of humanity (over another) is a form of nationalism. This can be almost anything (ethnicity, religion, race, etc.) The modern state (and its corresponding citizenship) is entirely based on nationalistic principles. Concepts like "American", "British", "Chinese", etc. only exist because they stand in opposition to rest of humanity (that is, "non-American", "non-British", "non-Chinese", etc.)