Disney is very clever. This is a huge plot twist. Also Elsa and Anna's parents did not die right away they floated to an island were Elsa and Anna's pregnant mom had tarsan and was eaten by the jaguar (For the Disney fandom)
But the ship that Anna and Elsa's parents took was the ship in The Little Mermaid. And wasn't Little Mermaid, like, thousands of years after Frozen? Nice theory, but you need to read some other theories first.