A bit more context, --> is shorthand for -[]->, so this is MATCHing on paths of a :Character node with a relationship (of any type) to any kind of node, then per character getting a count of rows. As a result per row we have each character and the number of relationships for that character (so num isn't an array, it's just an integer count, and we have a separate count per row/character). Then we apply aggregations over that count.