Hello,
you could send a note to the legal-talk mailing list:
https://lists.openstreetmap.org/listinfo/legal-talk
My judgement as a non-lawyer would be that it is not suitable, given they state " the data is freely available for humanitarian, or at least non-profit purposes."
OpenStreetMap is neither “humanitarian”, nor “non-commercial”. OSM data is used for all sorts of commercial purposes. Mapbox is selling the data as vector tiles. The OSM foundation is also registered as a commercial entity. No one can prevent me from extracting the Thai border and selling it for $$$ licensed as ODbL.
I also have the impression that the HDX people are not the owner of the data. They just forwarded data they received without clarifying the extent of the license.
So the right thing todo would IMHO be to contact the Royal Thai Survey Department and ask them for either a confirmation that their data can be included in OSM or even better asking them for updated data as well, maybe in colaboration to importing it. Potentially they have other boundaries available as well. Province boundaries or even smaller-scale.
Correct projection and other technical details to be considered before import is then a follow-up topic.