Response code 400 rather than 404

[lists at lazygranch.com]

I'm curious why this request got a 400 response rather than a 404. 

400 123.160.235.162 - - [16/Jul/2017:22:56:30 +0000] "GET /currentsetting.htm HTTP/1.1" 173 "-" "-" "-"

log_format  main  '$status $remote_addr - $remote_user [$time_local] "$request" '
                      '$body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';