Neville was completely unaware of his brush with danger there. He was used to fighting, to protecting himself and others, but he had always been reactionary. He waited until something was coming at him until he fought back. It likely put him in danger more often, in this case, more than he realized, but, despite his past, he never really liked instigating.
He frowned. He assumed she was trying to ask him something, just through the context and her expression, just visible by the fading light, but he couldn't figure it out and shook his head. He knew of sign language, but it wasn't particularly common among wizards, as far as he knew, and he definitely didn't understand it. He felt fairly unhelpful.