[Mesopropithecus]

In the intern's place, I probably would not have bragged about copying that company's idea.

Then again, as the company, if I felt a former intern could threaten my business like that, I'd ask serious questions about my value proposition and moat (which could be premium features, sales, or an attractive/viral free tier - not too familiar with what they do). On a personal level, I can see how it could feel unfair, but the idea does not seem that original.

[noncoml]

You cannot patent or copyright ideas. Furthermore it is quite debatable if it’s unethical to copy ideas.

What the intern did is absolutely fine in my book.