That's what they've said and there is nothing to contradict that beyond your own prejudices.
There are a lot of athletes. There are probably upwards of 100 athletes competing in the aquatic centre on any one day. If they each get 5 comp tickets (may be more, may be less), that's 500 seats that will probably only be filled for part of the day. Then add in seating for the teams and officials themselves, it is easy to see how so many seats are empty.