"A soft 404 error, on the other hand, occurs when the server sends a “200 OK” status for the web page, but Google mistakenly interprets the message to read that a 404 error should be displayed. Although it is a mistake on the search engine’s part, it usually happens when the page looks like an error."1
This makes sense as the Soft 404 happens on the /errors.html page and Google got confused (got 200 status code, but content looks to be an error).
"A soft 404 error, on the other hand, occurs when the server sends a “200 OK” status for the web page, but Google mistakenly interprets the message to read that a 404 error should be displayed. Although it is a mistake on the search engine’s part, it usually happens when the page looks like an error."1
This makes sense as the Soft 404 happens on the /errors.html page and Google got confused (got 200 status code, but content looks to be an error).