How do you get kids to tell the truth

A child walked up to my child look ready to hit him, made a fist and started talking to him getting in his face.

Started talking to him and my child was happy smiling and he looked upset after talked to that child.

I asked him what he said he said he didn't want to talk about it.

I want him to be able to talk to me tell me things. If he told me the other kid said something bad I could of talked it over with that other kid had him apologize and talked to his mother about it.

Also what should I tell him to console him if mean words were said bullying.