Yu Fei was outside providing support, so he had no idea what exactly Huo Sining and Gu Xu were doing inside that base. If he had known that the two of them had basically looted Tranleva's base, he probably wouldn't have been so calm.
When Huo Sining and Gu Xu entered the base, Yu Fei used a jammer and hacked directly into the base's system, then used imaging tech to reroute the surveillance video feeds, splicing previous footage into the next second so the security staff wouldn't notice anything wrong.
Once the surveillance footage was replaced by existing video, those cameras naturally became mere decorations, while the real recording data was directly deleted by Yu Fei's video rerouter.
Now that they'd already gotten what they came for and withdrawn safely, there was no need to stick around. Yu Fei quickly removed the video rerouter on his end, wiped all traces of the intrusion, and then the three of them packed up and left, clean and efficient.
