Harry was surprised to see what looked like a teenage girl step in the way before he could. While he still could've helped the woman, this girl got in the way. She looked like she was supposed to be a student. "That'll be your job," he said, "and you take yourself as well. This isn't a game, kid." Ever the hero, Harry didn't want to encourage the girl to stick around. The woman obviously needed some help and for someone to take her. Harry was an experienced wizard, a very experienced one. He needed to be here and doing what he could to help.
He shouted another disarming spell right after he spoke, moving quickly to shout out a few more and a couple of death eaters fell to the ground nearby, "Take her to safety and get yourself there as well." It was said as something of an order, even if Harry wasn't often authoritative. But when he had to be, he held his own and could pull it off. Harry wasn't unassuming, given his height of six feet and seven inches, but he wasn't burly or broad-shouldered.
But for a wizard, physical prowess rarely lent itself to being a distinguishing factor over who was better at magic than anyone else. For example, he knew the headmaster of Hogwarts was a formidable wizard and despite his years, he could hold his own among the best.