Earlier I had a permalink structure category/postname which I changed to /postname/. In my robots.txt file I had restricted one category with disallow: /abc directive.
Now that doesn't work as permalink structure doesn't have a category.
I went to category edit section in wordpress and selected Noindex this category: Always noindex and include in Sitemap: never include.
But still I dont see noindex tag in the code of posts under this category.