A bit of information here since the donghua didnt show it. The reason why Tan Yun moves behind the pillar and knew someone was coming is because as he was absorbing Heaven and Earth spiritual energy, he sensed that there was some disturbance in the flow coming from outside the pagoda, hence he knew someone was about to break into his room. And he was actually breaking into sweat as he ran outside since the attacker was at a higher level than he expected lol

Tan Yun flees in his spirit ship, but he loses control as Pang elder gives chase, the speed of the ship was so fast that when it crashed it causes Tan Yun a great deal of injury, so much so that people believe he is dying, and as Shen Qingfeng examined him, Tan Yun's heart stopped beating and dies.

But hearing the cries of Shen Qingfeng and other gardening disciples, Tan Yun restarts his heart. Before the crash he entered into a stasis, this is because by dying his life lamp is extinguished and so his enemies would think he is really dead

Elder Pang lost his left arm and had six broken ribs, however Lu Wu killed one of Elder Pang's disciple and took his arm using an extremely cruel technique, they were thinking of using the dead disciple's legs to replace An Bei's but because his legs were broken in public replacing it would draw a lot of attention and suspicion

Things will start to liven up :)

I thought the beams of light that spread out in the training room was like a spiritual net to capture the intruder like a defence mechanism because there was already someone in that room with a key and was like a warning system that warned Tan Yun at the same time.

In regard to the legs thing, I'm surprised that was even thought of considering medicine wasn't that great in the past and according to google search the first limb transplant was in 1998 but I have my doubts about that being correct. I would have thought they'd probably try to repair his legs as best they could and send him on his way since even walking may be difficult for him after.

I think that was the Heaven and Earth spiritual energy. but the novel did say that it was because he senses the flow outside was disrupted and and his senses felt something was wrong, kind of a bad premonition

Some Chinese Wuxia novels have limbs being replaced by cutting off someone else's lol I guess this is where it drew inspiration from, much like how Tan Yun has his technique of repairing broken limbs but theirs is considered evil since it requires killing or taking someone in order to be able to repair their broken limbs. lol Imagine taking limbs from a smaller person, An Bei will be shorter or have a bulky body with small thin legs lol

It's still possible even without limb replacements. Firstly, there are some medical issues which can lead to deformed growth in general not only for bones, but also muscles. I had something similar happen which led to my calf muscle being under developed compared to my other calf muscle but that was from surgery at a very young age which is why things like what I mentioned stick out to me. Also, there is also the option of someone only training their upper or lower body while ignoring the other half which leads to that too.

Ahh yes, I have seen people who has one side of their body is muscular and the other is normal, most of it isnt through gym but through daily work they do.

Of course there are also surgery in which people undertake in order to grow taller, this is done by cutting the shin bones and extending it by a few centimeters, some do it a few times in order to attain the height they want to, some of them end up with weak leg bones and is easily shattered

Actually I think I know where the confusion is, in the donghua Tan Yun breaks An Bei legs, in the novel, he actually rips his legs off, one of his legs was burnt into crisp, the other one was frozen and then shattered, An Bei was left with no legs lol

The last part reminds me of the bombing of Midgard in ff7...

Expensive Enhanced Training Building go BOOM!
Tan Yun (whistling nervously): "Oh really? Gosh! What happened? Nothing to do with me as I had just stepped out for a bit of fresh air. It was like that when I got back."

Imma need y'all to give Tan Yun a refund when this is done because he didn't cultivate for 57 days