This blogger is conducting a test

I want to see if posting through email really works. To that end, I present
the following observation:

The names of geometric figures are nouns:
"I have a triangle. I add a rectangle. I use a circle." See? All nouns.

If you want to describe something with these geometric properties, you have
to convert the noun into an adjective:
"I make a rectangular table. I cut a circular hole."

Noun : Adjective :: Triangle : Triangular

BUT! What about a square?
"I made a square. I like square sandwiches."

The noun and the adjective are the same!
What kind of messed up language is this?