What does that mean/how does it affect me?

It means that only people who have specifically turned "showdead" on can see your posts. No one can reply to you posts directly. Your upvotes do nothing and don't count. But crucially, to you, everything seems completely normal.

And howd that happen?

An administrator decided that your first ever comment didn't fit the tone of this site (which it didn't, but well, you were new), so they decided to instantly and silently ban your account forever. So you have been commenting, for a year, and basically no one has seen your posts. I feel really bad about that and I hate this objectionable practise.