This is probably because static content is added from files and those files are directly added in .phtml files.
Its also possible that content is added in current static block. ie we can edit new.phtml files to show some static content to display on home page.
This is not best practice but i saw many sites doing this and this is **STRONGLY not recommended**
You should remove that types of content and add static block as mentioned in https://stackoverflow.com/a/20948077/949003.
you can turn on template hint as told by @erfan.
System -> Configuration -> Developer -> Select a website or store view scope (current configuration scope) -> and turn on "Template path hints"