My assessment is based on my education and training in terrorism studies and countering violent extremism.
The National Consortium for the Study of Terrorism and Responses to Terrorism (START) defines right-wing and religious extremism in the following ways:
Right-wing extremism
Violence in support of the belief that personal and/or national way of life is under attack and is either already lost or that the threat is imminent. Characterized by anti-globalism, racial or ethnic supremacy or nationalism, suspicion of centralized federal authority, reverence for individual liberty, and/or belief in conspiracy theories that involve grave threat to national sovereignty and/or personal liberty.
Religious extremism
Violence in support of a particular faith-based belief system and its corresponding cultural practices and views, sometimes in opposition to competing belief systems. Characterized by opposition to purported enemies of God, nonbelievers, or perceived evildoers; striving to forcibly insert religion into the political or social sphere through the imposition of strict religious tenets or laws; and/or bring about end times. (Subcategories: Christian, Jewish, Islamic)
Based on what we have learned about Boelter and the definitions above, wouldn't you also classify him as a far-right/right-wing Christian exteremist?