The contradictions don’t matter. I think this brings flexibility to the development of a Django application. For example, if you’re using a third party library that defines some models, and they set blank=True, but for other purposes you need that field is mandatory, then in your forms you can fix it without touching the third party library code.
This just add some flexibility to the framework IMHO, that brings no harm. You can use it for your own purposes. The contradictions are not significant.
Hope this helps!