@rennov Here is my understanding. Wei has been retreating since Red Cliffs. Sun Quan been taking Wei's territories. Sun Quan sent the order to kill SIma Yi because this version knows how talented he is (Ch 533 pg 8). So Wu's forces been tracking Sima YI. Both Sun Quan and Liu Bei wants to take Jing, but they are technically allies through political marriage. So Pang Tong has been using the Tiger Generals dressed up as Wei soldiers to strike at Wu. I guess they will explain it away later by saying they recaptured it? Pang Tong arrived at the fort Sima Yi escaped to at the end of Ch. 535 after capturing the other location. Hence the last quote in Ch. 535 "Can Happen Again and Again" Referencing when Zhao Yun said the tiger generals sneak attack could only happen once. This time they are attacking Wei base, so they didn't bother to dress up as Wei soldiers.
In this chapter, Sima Yi been expecting the Wu forces, and set a trap to burn the base after the Wei soldiers escaped to the basements. The Wei base has mostly wounded soldiers, but Sima Yi still wanted to defeat Wu's army and break out of this area to return to Wei instead of just escaping by himself. I'm guessing these troops will be Sima's elite/loyal troops later. Unfortunately Pang Tong showed up and messed that plan up, but Wu has showed up following Sima Yi's tracks (the thing about scout upstream) and now things are getting messy. Lu Meng will most likely figure out Shu's been taking Wu's bases. More interestingly, if you know Guan Yu's fate, I'm expecting some heated moments between the two setting that up.