The word Innocent, in Spanish, has two meanings:
"Not guilty", how you say, is the first.
But, in addition, it means or how it is used synonymous with "unsuspecting" (incauto), "gullible" (crédulo) or "Naive" (Ingenuo).
Sorry if your no understand, I do not know if they are valid translations.
It is in this context that the word is used.
In other words, the "April Fool" were making jokes to the unwary or gullible.
This is good for learning cultures for others countries! 🙂
Greetings From Argentina!Pablo