Talking in Salah

Three people were praying salat in jamath. A man walks by and without knowing they are in salah says “Assalamu Alaikum”. One man in salat says “Walaikum Assalam”. The second person angrily says “Wastagfirullah, you are not supposed to talk in salat”. The third person praying says “Alhamdulillah, I didn’t talk.”