“The 誕 reading is what you’d expect. The 生 reading is an exception though. Just imagine the birth of your friend Joe (じょう). Pick a Joe you know well, or if you don’t know a Joe use a famous Joe, like good ol’ Joe Biden.”
Was Jourm on vacation when this mnemonic was written? Not that I have anything against Joe, but I think he’s kinda hogging the spotlight of the real star of the show here.