If Conditional for Lightswitch in Matrix Field
You're close! The way you have your conditional set up now will print Hero Image Markup if either of your conditionals fail. By checking if block.displayHeroVideo is 1 on a block type that doesn't have that field, Twig will still return 0. You should only check displayHeroVideo when you know you are inside of a heroVideo block. 

{% for entry in entry.heroFeatured.limit(1) %}
    {% for block in entry.hero %}

        {% if block.type == "heroVideo" %}

            {% if block.displayHeroVideo == "1" %} 

                &lt;h1&gt;Hero Video Markup&lt;/h1&gt;

            {% endif %}

        {% else %}

            &lt;h1&gt;Hero Image Markup&lt;/h1&gt;

        {% endif %}
    {% endfor %}
{% endfor %}