This summary is not the rule. The rule text controls.
Any side in a case can challenge a witness's honesty or accuracy, even the side that put that witness on the stand in the first place.
This matters because in the past, some courts made lawyers stick by whatever their own witness said, even if that witness gave surprising or unhelpful testimony. This rule gets rid of that problem. If you call someone to testify and they say something that hurts your case, contradicts an earlier statement, or just doesn't seem truthful, you're allowed to point that out and question their credibility just like the other side could.
In practice, this gives everyone in a trial more freedom to get to the truth. Lawyers aren't stuck defending every word their own witness says. If a witness changes their story, seems confused, or turns out to be unreliable, either side can bring that to the jury's attention.
