The Congregation for the Doctrine of the Faith’s Declaration on Masonic Associations states, “The faithful who enroll in Masonic associations are in a state of grave sin and may not receive Holy Communion.”
It is very likely that someone may not be aware of the Church’s position on Masonic associations. However, the CDF’s declaration does not state that those who are actively involved in the Masons are gravely wrong, but those who enroll are gravely wrong.
Given his most likely innocent ignorance of the Church’s stance on this matter, the individual is probably not in a state of grave sin. However, to avoid scandal that might give the possible appearance that Catholicism is compatible with Masonry, the individual should unenroll.