No, it did not focus on this because it's not something easily tested through an open playtest.
There are a few things they could test quite easily, though they might not be at that point yet.
The most obvious example I can think of:
Here's our suggested process for creating (or, indeed, advancing) a monster. Did you use it? Did you find it intuitive, easy, etc? In play, how did you find the monster compared with existing monsters of the same level? Any suggestions for tweaking the system?
Likewise for things like traps, environmental hazards, etc. These are all things that, presumably, the DM is likely to have to do at some point, and it would be good if they had some system beyond "just eyeball it".
So while I think the 'fluffy' bits of world-building, and the "good GM's guide" is indeed beyond the scope of a reasonable playtest, there are quite a lot of 'crunchy' mechanical bits that could be tested.
(I've been put in mind of this due to a recent experiment with 4e-style Threats for SWSE. And having seen that the 4e method works
very well, it would be good to think they're going to do something similar for 5e.)