Jibril said he feared none will enter Jannah after seeing it surrounded by hardships, and also feared every creation with free will will enter hellfire after seeing it surrounded by desires, mankind and jinnkind weren't even created then.. how did he come to know that multitude will enter jahannum? Given we have report only one in thousand will enter Jannah.
He didn't even know the actions of mankind or jinnkind on earth. Was it due to limited ilm al ghayb given by Allah or did he do qiyas?