The answer is a simple "yes." A person may be UNAWARE that his "personal Lord and Savior"
talk makes him a heretic, nonetheless, denial of Christ is the ultimate conclusion, the OBJECTIVE REALITY, the TRUTH of any dogma except for that taught by the Catholic Church founded by Jesus Christ. Whether a person is formally or materially a heretic, and how he will fare at his particular judgment are separate issues from the question you posed. Are you surprised you were dismissed by disciples of the greatest super-heresy, Vatican II?