You said a immature type grab for attention. Someone dating someone of a different ethnic group solely to get a reaction is similar, outrage is what they are after. I have seen both cases, not that there is anything wrong with dating someone from a different ethnic background, but knowing that the parents or whoever the person is trying to outrage has prejudices against it, then doing it just to rile them up while having little real interest in the person they are dating but more in the reactions they can get.
Its one of those classic ways to get back at or show up daddy, in many cases someone from a different class or a poorer background would do, but one of the best is race because its one of the worst prejudices to have and if you can use it, can have maximum effect.