It is very easy to shoot down friendly aircraft because they don't usually shoot back. They fly in nice straight lines because they don't expect to be shot down at any moment by their allies. They don't employ ECM against you. They don't terrain mask. But, maybe you are joking?

None of the other air forces involved shot down three F-15s, so I don't think it's that easy.

If I'm skimming this page [1] well enough (find: "shot down"), there's only 6 F-15s that have been shot down, and only 4 or them were air-to-air. If it's so easy, should be more than one other incident, and that guy only got one.

https://en.wikipedia.org/wiki/List_of_F-15_losses