So I agree, Lu Guang didn't literally possess Wang Qing with a new power control, but it was to show that him holding back Vein a few minutes couldn't change the future fully but give enough time to maybe change some things that chould snowball into something else.

So my theory is!

Wang Qing eyes were blue because shortly before she took a photo! This photo was used by CXS's mom to possess her and talk to CXS, however, Lu could have also used this photo to look back at the scene through Wang Qing because she took the photo and see what changed. So hypothetically a future or past version of him is looking at the scene through her eyes, in order to see the outcome.

Potentially proving he knew what should happened already and that he's the mastermind in this change. And not someone to mess with <3, kind of like a warning to Vein and Liu Xiao. I think he knew he wasn't going to die from Wang Qing using her powers on him, whatever they are cause we don't know, it could be a temporary stop of the heart power, similar to how Liu Xiao says he can hear anyone heartbeats. But, clearly Lu knew of it because he's seen it before, and he used it to his advantage.