They are in partial communion with the Church based on their baptism, but they are not members of the Catholic Church.
[quote=Pius XII Mystici Corporis]22. Actually only those are to be included as members of the Church who have been baptized and profess the true faith, and who have not been so unfortunate as to separate themselves from the unity of the Body, or been excluded by legitimate authority for grave faults committed.
[quote=Vatican II, Lumen Gentium]They are fully incorporated in the society of the Church who, possessing the Spirit of Christ accept her entire system and all the means of salvation given to her, and are united with her as part of her visible bodily structure and through her with Christ, who rules her through the Supreme Pontiff and the bishops. The bonds which bind men to the Church in a visible way are profession of faith, the sacraments, and ecclesiastical government and communion.
People can have other bonds with the Catholic Church other than being a fully incorporated member–we call these bonds “partial communion” (based on concepts enunciated by St. Augustine). Baptism is the source of that bond.
Here’s how Ott’s Fundamentals of Catholic Dogma explained it using the more historically common terminology:
Although public apostates and heretics, schismatics and excommunicati vitandi are outside the legal organisation of the Church, still their relationship to the Church is essentially different from that of the unbaptised. As the baptismal character which effects incorporation in the Church is indestructible, the baptised person, in spite of his ceasing to be a member of the Church, cannot cut himself off so completely from the Church, that every bond with the Church is dissolved.