What do people mean when they say that the "Fundamental Theorem of Engineering" is $\pi=3=e$?

Question

I've seen this kind of thing on many sites, that the "Fundamental Theorem of Engineering" is

$$\pi=3=e$$

Some of them said this is just a joke.

Well, I know $\pi=3,1415926\ldots$ and $e=2,7128128459045\ldots$

Then, what is the idea behind what did they thinking about?

Is this about "Rounding Numbers"?