Unrecognized IC Package Style

This might be the drawing for SOT804-4, which you are looking for. The land pattern is on p.3 .
The second row isn't soldered to the board, if I'm reading the drawing correctly.

I'm guessing, each oblique pad in the second row is connected to the pin on the outer row. So, the second row would be signals, not all grounds. If you have the an IC in your hands, you could check continuity.

p.s. I wonder what's the rationale for this odd QFN, and why a typical QFN didn't cut it.

Page 3 of that document gives you a land pattern. You don't have to guess.

In general, data sheets give you recommended PCB layouts, or refer you to documents (like that one) that give it to you.