Shor is angry and throwing things around.... But isn't Shor/Lorkhan dead?
So you haven't even begun to fathom this! I wonder to what extent you have even tried, because your issues with it are extremely superficial.
"Shor son of Shor" is a Dawn myth. You can tell because the Aedra don't do much of anything at any other time. Historical context helps as well, because fragments of this were posted in a thread about the dawn a year or two ago. You can also tell because it takes the form of the events of the Dawn, with the crucial distinction that should be confusing at first but only at first: in this story, the Eight Aedra are clans, within Shor's clan there is a character who shares their name with the Nordic name for each of the Aedra.
Why are mortal Nords mixing and mingling with Mara, Dibella, Kyne?...
There are no characters in this piece that I can find identified as "mortal Nords" - if by mortal you mean like the ones you find in the game. Nords, yes, but not mortal ones - ones with "scaled manes." They are, of course, still mortal in the sense that they can die; it is incredibly incoherent to ask how "mortals" could mingle with "gods" when you know that one of those gods has died.
If you cannot find an answer when you ask yourself why Michael Kirkbride would have called these characters "Nords," though, that's no one else's fault.
As to that last quote, that is the act of covenant. The Lorkhanic figure is made to be at odds with the other Aedra (in this case, the other Aedric clans) and loses his heart. This should be apparent.