I have a problem regarding the understanding of modulus.

So someone proved $5a + 2b \equiv 0\pmod 7$ is symmetric using the modulo circle,
and my brain cant comprehend how he meant that. I'm talking about circles like this:

[![enter image description here](https://i.stack.imgur.com/1nFvh.png)](https://i.stack.imgur.com/1nFvh.png)

I know there is a other way to prove it with $7 \mid 5a + 2b$