In a single sentence, difference between a line item and a list item is that a list item is a single dimension like country, product etc., whereas a line item can be a multi dimensional like sales for a country and a product by time.
As in the article, it says the dimensions are the measure to store data.
Because lists are single dimensions, you can store attributes of a single dimension like properties of a product etc. but a line item can point to multiple lists like product, country, time etc. and it will store values related to all the dimensions like 'x' number product is sold in America in Jan 2019 etc.
Best practice says that the list properties and attributes should be stored in module with a single dimension of that list.