Well he may not be feeling sad but he will be expressing some emotion. Then you validate that emotion:

"So you feel angry because xxxx"
"So you feel embarassed because xxxx"

He may say I am not sad/angry etc but you just keep trying to work it out so they feel that you get them.

Youre not telling them how to feel. You're reassuring them you understand; you hear them; and you accept them and their emotions. It's a very freeing thing for the child and sets them up to know and feel that they can come to you for any problems they may have, and you will be a good listener and help them feel good.

Its like the example how many times have you vented to someone, let it all out and went on and on about something, the other person barely said a thing but you felt so much better after? Once you release the pressure or stress you are free to more effectively deal with the problem in a place of calm than stress - we all know that means better decisions.