Hypotheticals could fill the grand canyon - but in the case of an infant - generally speaking - the parents make a citizenship decision until the child reaches adulthood.
In the case of grants of citizenship by many countries (including Canada) the parents cannot “renounce” the grant for their child, it can only be confirmed by the child when they turn 18. If the child does not confirm, then the grant is removed.
Again, why would the actions of a foreign nation - independent of the wishes or desires of the citizen or their parents - matter in terms of who we consider a citizen? How is what you proffer different from having Hugo Chavez unilaterally grant any US Presidential candidate Venezuelan citizenship?
This isn’t a hypothetical; this is a real issue, that happens to real children every day. What a foreign national considers you to be should be irrelevant; what matters is what you (or until of legal age, your guardian) and the United States consider your citizenship to be.