as mentioned in the title my WordPress blog has this URL. which is not familiar to me. that not a GET request right? what is that? please help.
Your question is what kind of URL is this
The answer is: It's a valid path.
A valid URL path can contain any of these characters:
a-z A-Z 0-9 . - _ ~ ! $ & ' ( ) * + , ; = : @
That means .php can appear anywhere in the path - something we recognise as a php file extension.
If someone makes a GET request (the request type is set by the client and can be any type permissible in your OPTIONS) and this is processed as an URL path, it will look in the blog/index.php/author directory for any configured default files (like index.html, or index.php).
However, your server might be trained to filter for ~.php~ in the URL and pass the path fragment to an interpreter. This means index.php is being called with the path fragment /author. Your Wordpress configuration might be making internal use of this.