As is stated repeatedly on this forum, it all depends on the school. But, let us speculate and overgeneralize. If you did not already hold a Master's, then this would be perfectly normal. Since you do, they may have made that decision simply because it is out of field, as you have guessed. At the end of the day, the courses will be the same and if they will be applied toward a PhD after qualifying, it doesn't really matter. The only thing it might affect is funding and time to completion. Otherwise, congratulations on your acceptance! I'm sure you will progress smoothly through the Master's portion and qualify for the PhD program.
Did they indicate how long it might be before you can apply for or qualify for the PhD program? And how much coursework is required for their PhD program? I know in the British system this type of situation is quite normal and usually people can spend 1 year in the Master's program, apply to the PhD program using the Master's work to fulfill the coursework requirement in which case, there is no time lost or wasted.
To answer your final question, I am also applying to Ed. Policy programs and I do not feel good about attending without a guarantee of funding in the form of at least a tuition waiver.