He had much the same reaction when he watched Xiao Xingchen walk off the platform the first time. He doesn't particularly like seeing this transfer himself. They might not have been considered friends but they had started to get along at least slightly. And he owed Wen Qing for saving his life. To see her walk off is frustration but not nearly as much for him as it is for Lightning and he knows it.

"I know that didn't feel good. I've had experience with that."

Meaning more the hand meeting the train then losing a loved one.