What is the NAT traversal technique used by bitcoin https://bitcointalk.org/index.php?topic=30947.msg23736281#msg23736281 says that 


incoming port can be opened or 
UPnP enabled.


Is this incoming port opened on the NAT device so that all incoming messages coming to that port are relayed to my host?

EDIT: More resources about the topic https://bitcoin.org/en/full-node#enabling-connections and https://bitcoin.org/en/full-node#network-configuration

The second resource says: "If Bitcoin Core can’t automatically configure your router to open port 8333, you will need to manually configure your router." 

Is this automatic opening mentioned actually UPnP way?

And manually configuring the router actually bullet 1 mentioned above?
Is this automatic opening mentioned actually UPnP way?


Yes. UPnP is disabled by default in Bitcoin Core due to some vulnerabilities in UPnP. You can enable it by going to Settings &gt; Options &gt; Network and checking Map port using UPnP


  And manually configuring the router actually bullet 1 mentioned above?


Yes.