China likely has nothing to do with this. It is unlikely they have any participation or even knowledge of this. Twice now some Russians in a China flagged ship caused trouble, and the China-flagging seems very intentional.

Russia is desperately trying to make the China-Russia thing a reality, and is probably trying to drag them in against their great resistance. China has zero credible reason to be dragged into Russia's nonsense, and a billion reasons why they want nothing to do with it.

The ideal outcome of this is that China realizes that Russia is outright trying to drag them into conflict, and that they repudiate that country entirely.

China has already been involved quietly, funneling weapons and intel to the Russians, essentially playing the opposite role to the US. Make no mistake - this war has a component of the US and China probing each others' capabilities.

The Russians could have done this with a fishing trawler (they cut cables accidentally all the time), so like you I doubt we can infer some nefarious Chinese plot from the flag on the vessel.