Don't get hung up on "patent". You can't patent an idea, you patent a specific implementation of an idea.

The boy experimented to find the optimal parameters (height, width, angles) for load bearing of that earlier invention.

So, the result of his work would warrant a new patent, of course with reference to all earlier patents of which his work is an improvement.

You can even spend time and money to acquire a patent and it still doesn’t guarantee profit. It’s called the Miura-ori even though it was patented decades earlier. In this case, the patent acts as a record emphasizing that it’s all been done before.