There absolutely is a legal transfer. the donation assigns copyright, and normally includes the intellectual property rights of the trademark and logo.
In theory, the recipient could choose to relicense.
In theory, the recipient could choose to relicense.
Despite the fact that there most likely is some transfer of intellectual property contemplated here, I do think the term "donation" is a little odd when describing stewardship transfer of open source projects to nonprofits -- though it's fairly well established (I associate it mainly with the Apache Software Foundation).
To me "donation", based on its ordinary usage in English, suggests "here's something I don't need anymore; you can have it, I won't have any further involvement in it." That does fit certain situations (an example that comes to mind is Oracle's transfer of OpenOffice to the ASF).
But it all a very open-source-oriented, metaphysical concept, in that by giving up some control over a project, the company that originated it is hopefully going to bring in many more contributors and ultimately increase both the total value of the project and the value to them. A core CNCF value proposition to projects [0] is that: "A neutral home for your project increases the willingness of developers from other companies and independent developers to collaborate, contribute, and become committers."
Solomon made a useful analogy [1] that "rough comparison: Docker EE=RHEL, CE=Fedora, containerd=Linux".
[0] https://www.cncf.io/projects/ [1] https://twitter.com/solomonstre/status/837313258252091393
Disclosure: I'm the executive director of CNCF and have been working with Docker on their contribution of containerd and with CoreOS on their contribution of rkt.