Lead Developer
The first point on that page says this:
Page templates only apply to pages, not to any other content type (like posts and custom post types).
You can load scripts/PHP code on some posts or pages by using if conditionals: https://codex.wordpress.org/Conditional_Tags
Specific pages: https://codex.wordpress.org/Conditional_Tags#A_PAGE_Page
Specific posts: https://codex.wordpress.org/Conditional_Tags#A_Single_Post_Page