A lack of such a prompt would mean nothing from security point of view. It's not like you run a program you used regularly and now all of a sudden such a warning appears (as if someone replaced the program's binary with another one). You did download this program manually from the internet, the warning is basically just about that.
Yes, but the target group of this project is not "me". It's potentially many people, and I assume (maybe incorrectly) that the author wants their project to succeed and gain traction.