Being that we have made Black and African American synonyms when they're not. It's very possible, and very common that the person is saying they're not african american or that they're AA+PR but because we use the terms interchangeably, it becomes a tricky thing for folks to navigate, so they do it clumsily.

This is not to say that Puerto Rican culture isn't rife with anti-blackness which plays a role as well. But just something additional to consider in these situations.

Also, the conversation on race in the US IS lightyears ahead of Latin America. Partially due to the one-drop rule vs the miscegenation and racial mobility of latin america, and partially (and it could be argued these things are related) because there was never a civil rights movement in Latin America.