Yeah I watched Hidden Fortress recently and a Lucas interview about it. There are other similarities (a princess, etc.) but if I remember correctly Lucas said this was coincidental. He didn't talk about it, but the older hero has a duel midway through and I'm almost certain that was an inspiration (the way it's shot, the soldiers looking on, a prior relationship between the challengers).
Of course Kurosawa's influence was more than just plot points.