Hey, Parkin, good to see you 'round these parts again! :-)

But yes, I agree; I am also confused. In a mirror image, the letters are reversed, as in b becomes d, etc. But a line printer (tsuwm?), though it may print boustrophedonically, has each letter facing the right way, with the words spelled forward not drawkcab.
rotated 180 degrees would mean either that the either the individual letters or the entire line would be in reverse, it seems to me. Like this:
:siht ekiL .em ot smees it ,esrever ni eb

tablets where the alternate lines use rotated glyphs. People wrote like that? Chiseled, or whatever? Whoa!