An announcement does not indicate that the page actually has become a policy, guideline, or style guide. An announcement only indicates that a category has been added to or removed from the page. In some cases, this is because the status has actually changed. In other cases, it is an accidental change that can be easily fixed.
No automated script can tell why the status changed. The bot's messages are only intended to bring broader attention to a change. The bot task is completely automated and isn't meant to express any opinion about the status of any page.
Discussion about the actual status of a page should ordinarily happen on the associated talk page. It's polite to post a short response below the bot's announcement, especially if the change was accidental. This lets others know whether to spend time investigating or discussing the change.
The bot uses category membership to obtain lists of policies, guidelines, and manual of style pages. It makes no different whether categories are assigned by a template or directly entered in the page source.