How do seedless watermelons still develop full size seed holes in the meat?

Question

Holes are fully developed without a seed to push it open.

Answer 1

They aren't truly seedless. They have those white to translucent, small seeds that are really just the outer coats of seeds. Occasionally you will see a black, fully formed seed. Also, seedless watermelons are hybrids of seeded and seedless varieties and the fruit still tries to produce seed, hence the spaces.

https://www.gardeningknowhow.com/edible/fruits/watermelon/seedless-watermelon-plants.htm