Yeah, it was ludicrously forced in its attempt at political correctness. I'm struggling to think of same-race couples at all. Even Donna's fiance in The Runaway Bride was black.
The BBC had a thread of programmes about this a year or so ago, the reason was because The United Kingdom has the highest percentage or has one of the highest percentages of inter-racial couples in the World.
So in the case of RTD, it wasn't being shoehorned it nor was it pandering to the PC brigade, it was simple fact and he was acknowledging this.