was it a good idea to fire him for losing friendly matches?

@poster
Where's you link?

If the story's true though, yep, I think it's a good idea.
The purpose of friendlies is self-test. . .see just how good your team is, note areas that need improvement.
If you can't win any, it says a lot about the state of your team.

Anywayz, I've watched the Bafana Bafana dudes play before. They are kind of okay, but they severely lack proper finishing skills.

The team lack finishing.It just does not exist.