The blue dot seems to make sense as it represents the world without focusing on one perspective or projection of the world map. The transparent background also makes sense for the flag, but I think it would be more recognizable if it was just a white background (in my mind the default flag background).
Also it seems to me transparent materials are in general more polluting. On the website it mentions a black background was considered (I suppose representing space). It would be nice if there was an alternative version chosen without the transparency for mediums where transparency is not an option either black or white would suffice imho.
As others mentioned it does seem very similar (same proportions) as the Japanese flag. I wonder what the opinion of the Japanese is on this concept.