What constitutes a 'Wonderful Word'?
I sent a mail to the developer of the game to ask how this message is triggered. Here is what he answered about this feature:
If you score (in average, based on past stats), less than 0.3 bingos per game, a "wonderful move" is triggered whenever you score more than 30 points. Otherwise, you are considered an experienced player, and you need to score more than 50 points to trigger the pop-up.
So it seems you got the pop-up there because you scored exactly 30 points with the word 'JOE', and you have an average of bingos per game below 0.3.