Anxiety Is Simply Unexpressed Anger

I just read the above line in "The Great Pain Deception" and didn't really understand it, so I looked it up.

Here is an article I found which explains it somewhat:

https://www.psychologytoday.com/intl/blog/anxiety-zen/201607/the-surprising-emotion-behind-anxiety

I still don't fully understand this. How can unexpressed anger turn into anxiety? Can anyone explain? Or are there any other resources that explain this process?

I must have repressed anger as I am one of those people who doesn't get angry often (apart from at injustice, and I DO express my anger then!), and I have TMS and the TMS personality traits. But I actually don't have much anxiety either. I'm not a "worrier". I do have some anxiety around specific things like setting boundaries and certain types of conflict (and I know where that comes from).

But why would those things have anything to do with anger anyway? Is it because it is "normal" to feel angry if someone starts conflict with you? I usually just think a person who does that has their own stuff going on and I needn't waste my energy on it because it's nothing personal. It only gives me anxiety if feel I really should confront a person over something.

So confused!