From the article: "PEN America defines a school book ban as any action taken against a book based on its content and as a result of parent or community challenges, administrative decisions, or in response to direct or threatened action by lawmakers or other governmental officials, that leads to a previously accessible book being either completely removed from availability to students, or where access to a book is restricted or diminished."

So I'd say it's more than "parent complaints". The books under discussion are not accessible anymore according to PEN's definition.