Why cache form table gets new entries by anon page views? I am seeing new entries in my cache_form table when anonymous user view a page that had a comment form. The page cache is enabled and set to 30 min. Does this mean that cache page is being bypassed? Or does drupal cahe forms for every anonymous user using a hashed key?     

Also I should mention that this happening for forms called and renderd in the theme layer (someone's mistake and I'm trying to correct this) .
Comment form is a form. All forms generate entries in form cache. Form engine uses cache as it's temporary data storage, not as the cache in usual definition of the word.

One thing it always store is a list of fields it actually displayed to a client, so it can compare it with a list of values that come back and prevent hijacking and other abuse - hence one entry per user session per form.