I think maybe you are confusing “kind” page and a section named pages that will have type pages?
So type page I think will miss layouts/pages/ and looks for single.html in _default/ or layouts/page/ ?
I have strange Hugo behaviour.
I changed “pages” section into “staticpages” section and settings.
While Hugo server is running, I removed “type” from frontmatter in staticpages/pagename.md and Hugo used proper template.
However, after restart Hugo server, the problem came back, so Hugo take template from the “posts” section.
To remain current folder structure is:
theme/layouts/_default/list.html and single.html and baseof.html
theme/layouts/staticpages/single.html
theme/layouts/index.html