Here is a quote I found in the article: "The decision dictates whether the securities are designated as “held-to-maturity” (HTM) assets " - HTM was an internal designation - an accounting convention. It does not have anything to do with the bond terms.
I'm not an expert. But it appears to be an accounting designation that shows up in filings, so it's not purely internal. You are correct that they are not part of the bond terms, which I was unclear on before.
"HTM assets are not marked to market... they remain glued to balance sheets at amortised cost regardless. By contrast, AFS assets are marked-to-market... Sell even a single bond out of an HTM portfolio, however, and the entire portfolio would need to be re-marked accordingly."
