Viruses cause colds. They cannot be affected or cured by antiobiotics. Bacterial infections can be treated with antibiotics. Chances are that you had a secondary ( bacterial ) infection which did respond to antibiotics, but he has probably got something else. Does he smoke ? How old is he ?
Does he get pink spots in his cheeks which he didn't have before ? Does he get night sweats ?
Those last 2 symptoms might suggest TB. An Xray would show up either TB or cancer.
TB can mostly be treated, can mostly be cured. Most lung cancers will end up fatal.