"invented" / "hacked" In the interview he said it was something he threw together in 20 minutes, so clearly not something groundbreaking / super involved, so probably more journalistic interpretation rather than his own claim. If he did use the word invention? He's a kid.
But props for curiosity and hacking at tech. 99+% these days are reduced to passive consumers. I did pretty much the same, ripping the radio part out of a clock radio and using the trigger wire from the clock board (that used to power/turn on the radio part) to switch a relay so I could instead turn on my big stereo system.
as to the power sources - clearly the original clock was mains powered with a battery backup to keep the clock going and possibly powering a buzzer, so that you don't oversleep if there was/is a power failure. Pretty much standard for alarm clocks / clock radios...