> The project is Apache licensed, so even if they took it, outside of lacking attribution / retaining copyright, I don't see a problem? They would be require to add it to an "About" tab or something.

They used it without having a license. The apache license would have allowed them to use it, but they didn’t meet the conditions.

This sounds equivalent to using paid software without paying to me.

The original author could well claim that “the cost of a license under the terms which they used it is $2M”. After all, the cost of software licenses is entirely arbitrary and set by the author (copyright owner).