Google states the what I copied below. However, they may have been leftovers that have not been crawled since you made the changes. Sorry- I didn't think of that...
Usually, when a visitor requests a page on your site that doesn’t exist, a web server returns a 404 (not found) error. This HTTP response code clearly tells both browsers and search engines that the page doesn’t exist. As a result, the content of the page (if any) won’t be crawled or indexed by search engines.
A soft 404 occurs when your server returns a real page for a URL that doesn't actually exist on your site. This usually happens when your server handles faulty or non-existent URLs as "OK," and redirects the user to a valid page like the home page or a "custom" 404 page.