Geez, I'm glad you're not war minister. It's a Chinese registered ship with a Russian captain.
If a terrorist crashes a truck with Portuguese plates into the US embassy in Berlin, would that mean Portugal's declared war against the USA?
China may back Russia to try to shift perception of the west's military might/will or to drain resources or just to buy Russia by making them dependant to get those juicy Russian natural resources but they aren't going to start world war iii to help Putin with his fetishistic "yet another European dictator" fantasy.
The Chinese know how to play the game same as the Russians and the US. All these little games are just calibrated psyops, why destroy, very publicly, comms lines when tapping it would be far more beneficial to a war effort and much quieter? Maybe to make the West look weak and unable to defend their borders which affects consequences domestically like say channeling political support to isolationist politicians who want to retreat from supporting Ukraine? Cause those politicians didn't make gains in the last European elections or nothing.