I believe there is a typo in the article.
Unlike dynamic array & queues an associative array can have index as any data type ( Eg: string / enum )
bit [7:0] array_enum [tr_type]; // index type is enum type
bit [7:0] array_string[string]; // index type is string type
bit [7:0] array_int [int]; // index type is int
Associative arrays also support wildcard * as index
A few references on it