Judging by her response the ratbug was doing exactly what it looked like, trying to harm or kill the girls. Once one of the girls thanked him for his help he simply nodded and said "You're welcome". But then as he was on his last wipe of cleaning the blood off his blade she asked who he was. So he stood up, putting his sword back in it's holster and said "I am Gwazi Magnum". He was somewhat reluctant to give more info, seeing as he had no idea what their intentions were. But considering they just got him out of the tight spot he was in with that rat bug, combined with the fact if you want people to trust you, you need to be honest. He decided to elaborate further and continue with saying "I'm just wandering by, so I happened to be sleeping nearby when that... ratbug thing showed up".