Please help :'-( my parakeet baby ped away?

My dads friend found two little parakeets sitting outside one day nd was able to capture one of them. They were very young but able to fend for themselves nd eat seeds. We took him in nd had him for 11 days..... He randomly ped away one morning. I would like to know why. He was soooo happy nd cheerful nd came out to play nd snuggled with us.... My parents said they heard him chirping under the covered cage in the morning.... Around 6 in the morning nd a couple hours later they uncovered the cage only to find him.... Ped away... It kills me inside because I was with him constantly nd he finally got use to us.... Why did he leave us? He was the happiest bird.... He played nd chirped nd there was no sign of sickness.... Please help us find out why our birdie died :'-(