I think HN tends to undo all caps words unless it's an acronym HN specifically recognizes. Guessing BGP, GRE, and FreeBSD are understood but AS is not.

It’s too late now, but when submitting a post the poster has a window of time to edit the title. Useful for example when HN auto-edits to capitalisation get some words wrong. When you edit the title, those auto-edits are not applied to your edited title.