Maybe not fair, but a logical conclusion based on three facts; (1) Richard Williams' attitudes and statements about the flag, (2) Richard Williams raised Serena, (3) Serena sat on the flag.
Serena Williams sitting on the U.S. flag could mean a lot of things; (1) she was too giddy to notice, (2) she is too ignorant to know any better, (3) she doesn't care one way or the other because that's the way she was raised, or, (4) it was intentional and she was expressing her contempt for the U.S. flag taught to her by her father Richard Williams.
In view of Richard Williams' comments, number (4) seems the most likely, (3) and (2) also quite likely, and (1) not likely. If Richard Williams had carefully instructed Serena in matters of patriotism and flag etiquette, it's doubtful she would have sat on a U.S. flag, let alone sit on a U.S. flag dragging on the ground.
It looks like whoever put it there had no clue in the first place.
This seems like a good explanation. Whoever put the U.S. flag on the ground for Serena Williams to pose sitting on, also had other national flags dragging on the ground. But, if Richard Williams had carefully instructed his daughters as carefully in matters of patriotism and flag etiquette, as he probably did in tennis etiquette, it's doubtful Serena would have done this.
Look how far down they placed the flag. Looked more like a quick photo op.
I'd say two possibilities for this; (1) a staffer working for Australian National Open and photographers from the press pool set up the photo opportunity with the flags dragging on the ground and didn't know any better, or (2) a staffer and photographers wanted to make a negative statement about flags.
I wonder if William Carney would kick Richard Williams' ass.