I just tested that out, and as long as the keywords are entered in as "word, word, word, word..." the plugin counts them correctly. If you don't add a space after each comma, the plugin considers them as one word. So, add a space between the comma and next word.
*I edited the language file to change the registered only message. However it will be better if you add a place for overriding default message in the plugin backend.
Thank you for your review and the suggestion!