fastcgi cache seems to be working weired

i tried to follow the document https://rtcamp.com/wordpress-nginx/tutorials/single-site/fastcgi-cache-with-purging/ to set up a wordpress blog with nginx fastcgi caching and added nginx helper plugin help me with cache purge. I am on debian jessie. nginx 1.8.0, nginx cache purge 2.3, php5.6 wordpress 4.3.1 and a plugin autoptimize 1.9.6. but looks like only my home page (say https://example.com) is getting cached and not other pages (say https://example.com/sample-page/). any help here will be highly appreciated. nginx helper is doing a great job with respect to cache purging.