Hmmm, I was just reading a book where it was pointed out that the scots used lighter, smaller horses, mostly during warfair, and often used no reins; controling the horse with their feet. However, that was in a time period before this, I am guessing.
Yes, it's true that Highland ponies were typically smaller (and shaggier) than other European breeds. And it's typical of many cultures that they would be able to ride into battle by using leg cues instead of direct reining so that their hands were free for weapons. However, for most regular riding, a combination of leg pressure and reins would have been used.