The only reason I assumed it was because it said on"occasion", your most likely right, and I agree 16 is not very old for a Pacu.I don't think he feed it light bulbs... More likely an accidental ingestion. My pacu will chew/swallow anything their mouths come across. They'll even chew up emergency air lines. They are extremely curious inquisitive fish. Not having hands, they use their teeth and mouths to check everything out.
From the reading I've done 16 yrs is not a long life for a pacu.