Yes, I agree that the filename should start with an underscore.

I had the impression that you were debating against / asking for explanation on the pattern of matching scss files to view files, hence the explanation.  If you're happy with this pattern, no problem.  If not, we probably need to have a discussion and review the Whitehall styleguide: https://github.com/alphagov/whitehall/blob/master/docs/css.md#views (which should be updated anyway to reflect that all scss partials start with an underscore).