However I especially didn't understand why some of the values under Privacy > Traffic / DNS Traffic say "NO" but are still in green. Or why some of the other values under the same Privacy column like "connection" say "Yes" but are in red.
Can anyone explain what those mean? Also does empty values there mean "no data available" or something else?
I think you are talking about Column E (Privacy->Logging->Activity->"DNS Requests") ? Since it falls under "Logging", you want it to be Red for YES & Green for NO (you don't want your VPN provider to log DNS Requests, etc). You will notice that everything within the "Logging" columns (Col D-H) follow this color coding, whereas for Col J-M (which are still under "Privacy", but the subsection is "Activism") it's opposite.
This chart was compiled by reddit user ThatOnePrivacyGuy.
Those say no and are green because they do not log traffic/DNS, which is good. Very simply, green means good and red means bad.