Access the row level field of a image field with multiple values
I'm the author of the Starter module you reference. I've made a change to the get_image_path() twig extension, in order to support images in passed by these means.

In order for this to work as required, you need to change your view - under Multiple Field Settings for your field, tick 'Display all values in the same row'. This will ensure that the fields aren't output as a multiple of the total number.

Then, in your view fields template, use:

{% for item in row._entity.field_header_images %}
  {{ get_image_path(item.getValue()) }}
{% endfor %}


Hope this helps.