Over a minute had passed since Sato and Cecilia had started exchanging blows. Rather than calling it exchanging, it was more of Cecilia attacking with Sato running around the place as he tried to dodge. Cecilia didn't give him any breathing space to counter so Sato was always forced to be on his feet lest he gets injured. However, it wasn't like there were no gains in this for him.
Having survived for this long, Sato became confident in his suspicions. Cecilia couldn't use her full strength. Otherwise, he wouldn't have had any chance to react and would have been dead long ago.