where did these come from?

The principles represent what the Foundation, as a business entity, will not do. They do not in any way represent what various portions of the greater movement shouldn't do. I know you understand the difference but I'm going to spell it out a little here in case anyone reads this who's new to the process and might not :-)

The Foundation, itself, has a limited staff and has to set particular priorities. The movement, which is made up of the various volunteers in the Wikimedia projects as well as other interested stakeholders, can set its own priorities - those priorities are usually fluid and dynamic and based (correctly) on what particular editors wish to do.

In this case, the Foundation is saying "we're not going to engage in this because we believe that either it's not the right time, outside of our mandate, or we believe there are others who are better qualified to engage in these activities". A good example is the museum collaboration you mention: chapters have been enormously successful in doing this. I think everyone involved with them recognizes that the chapters do this with a high degree of excellence, and the movement is best served by the Foundation staying out of the way of the people who do it well.  :)

As for how official these are: the principles were presented by Sue to the Board, and my recollection (which I just tried to confirm with minutes, but can't seem to find on the website) is that the Board voted to approve them. I could be wrong on the vote to approve... it could have been a resolution accepting them or some other thing, but there was definitely a Board discussion of them and a broad agreement.