In Spanish, it's common for double negatives to not actually be double negatives. For example, if you wanted to say "there's nothing here", you'd say "no hay nada aquí", which word-for-word means "there's not nothing here".
Checking out the Royal Spanish Academy, here's what they say about it:
> The so-called "double negation" is due to the obligatory negative agreement that must be established in Spanish, and other Romance languages, in certain circumstances (see New Grammar, § 48.3d), which results in the joint presence in the statement of the adverb no and other elements that also have a negative meaning.
> The concurrence of these two "negations" does not annul the negative meaning of the statement.
Checking out the Royal Spanish Academy, here's what they say about it:
https://www.rae.es/espanol-al-dia/doble-negacion-no-vino-nad...
> The so-called "double negation" is due to the obligatory negative agreement that must be established in Spanish, and other Romance languages, in certain circumstances (see New Grammar, § 48.3d), which results in the joint presence in the statement of the adverb no and other elements that also have a negative meaning.
> The concurrence of these two "negations" does not annul the negative meaning of the statement.