It's possible:
* It's a local or internal style guide: Some news organizations or specific publications might use the term "Five Boxes" internally to refer to a particular structure for their articles. This structure would be unique to that organization and not known outside of it.
* It's a misremembered or informal term: The person who mentioned "Five Boxes" might be approximating a known style, perhaps referring to a structure involving five key elements (like the five Ws and H – Who, What, When, Where, Why, and How). However, the "boxes" metaphor suggests a visual or structural organization, possibly a layout with five distinct sections in a printed or online article.
* It's a misunderstanding: There might be a misunderstanding or miscommunication regarding the terminology.
To understand what someone means by "Five Boxes" style, you'd need to ask them directly for clarification on what the five boxes represent in their context.