Any comment you receive from anyone you do not know that states you need more keywords is spam.
Any comment you receive from anyone you do not know that tells you you need SEO help is spam.
There are not only robotic programs posts that spam but there are human beings who are hired to post that spam and other spam. Trackback and Pingback Spam: What to do?
What Are Keywords?
Pretend you are in a Library looking for a book on learning photography. Well "photography" is a keyword. Pretend you are interested only looking for books on landscape photography. Well "landscape photography" is a keyword phrase.
In other words if you know how to use a catalog in a library or a search utility then you already know what keywords are. In any language keywords naturally occur when we speak about any subject like photography or anything else as we repeat that keyword when discussing the topic with others.
Do not get into keyword stuffing as Google spiders detect it. Assign only the minimal number of relevant Categories and Tags to your posts so they won't be "missing posts".
Do read this thread for advice on assigning Categories and Tags to posts.