Unless the terminology has changed, a line printer does not print boustophedonically; it prints an entire line out at one time. Printers with a single character at a time print head will print from left to right and then right to left, but the result is not boustrophedon. It's just normal read from left to right (or right to left, depending on the language being printed, e.g., Hebrew or Arabic). As to the original question the term refers to both miror image and upside down. We don't have to decide on one or the other to proclaim it boustrophedon.