Entity-Relationship Diagram Software
Perhaps unsurprisingly, you're not the first person to be intrigued by the fancy, fancy pictures in that post. If you look at the comments section below, you can see user @dangerousdave asks...


  nice diagram, what tool did you use?


...to which the poster @joel-brown replies...


  ... I use Visio with custom smart shapes that I built to use the James Martin ERD visual convention and a custom line pattern that gives it a hand-drawn look.


You might try reaching out to Joel at his public contact info and asking if he's willing to share the extensions he used (although the original post is around ~6 years old at the time of this writing so don't be too disappointed if he's using something else by now).