You're right that it's oversimplified, but your alternative isn't better. Horizontal lines are lines of type, but vertical lines are container borders? Simply using 4 or 5 rather than 3 horizontal lines would be best.

Also, FTA "Twitter Bootstrap refers to it as “icon-align-justify"

Actually the latest version of Font Awesome has three line icon for "icon-reorder" and four line icon for "icon-align-justify"