The developer was obviously brain-picked for any implementation ideas, as stated at scale. They should have been paying a retainer, or had an offer inside of two weeks.
Let this be a warning for other developers.
Paintings are just paint on a canvas, and all code is just clicks on a keyboard. That doesn’t make it any less immoral to blatantly copy without recognition.
It’s perfectly fine to carry out a fork, the irony here is that Microsoft likely tried you play this angle of “we’re just competing, not copying you” because they thought carrying out a fork with attribution would blow up in their face, which this now has.