As typically used, the term "shadow banned" is a ban without alerting the user that they are banned. That's not the case here. On HN, "banning" means to to have your posts be dead by default. And "banned" is the language 'dang himself used in the message to the user.

We banned your account for breaking HN's rules, as I explained to you when I banned it: https://news.ycombinator.com/item?id=29127479.

It has nothing to do with your particular statement about gasoline taxes or anything else. You could have made exactly the opposite statement and it would have had the same effect. The deeper issue is that HN is not a site for people who want to defeat their political enemies; it's a site for people who want to have curious conversation and learn from each other. I don't think that's too hard to understand.