What you describe is the entrance to their esophagus. That's why although the kayaker found himself in whale's mouth, the animal could not swallow him and had to spit him out.
To add to this, what you're both describing is true of Baleen Whales, which are filter feeders (which includes the Humpback Whale that this story is about, as well as Blue Whales and others).
But it's not true of all types of whale - Toothed Wales (such as Beaked Whales and Sperm Whales) are apex predators which much larger throats allowing them to eat larger prey.
The whale must have been aware of the size of things it can swallow?
Maybe the whale read Pinocchio and it wasn't just by accident?
Maybe the whale was playing?
Maybe it was a game about dominance? Maybe it was sexual for the whale?
