Ok, how about this: every knight was a man at arms, but not every man at arms was a knight. But one could not tell apart the noble men at arms from the non-noble men at arms except by their heraldry. And peasent levies? That's fiction, if an army had a large portion of poorly armed peasants then it was a peasant uprising, and even they would be well armed and led by nobles. The last medieval peasant uprising in Europe was in Finland, called a "club war", but it turns out they were led by rich estate owners and equipped with plate armour, arbalests, cannons and the works.