No it isn't.

Both of the two Chinese registries are open, pretty much anyone can register ships there. It's a bit like the .tv domain — if you see something.tv you can't assume that it's a company in the country Tuvalu.

Look at the nationality of the captain and the beneficial owner instead.

That would not swing.

Denmark controls the waters of the seaway to Sct. Petersburg and Kaliningrad that are some of the strategically most important ports of Russia.

Blocking of traffic to these would be a severe escalation.

Regularly Russian subs pass through Danish waters - controlled and allowed.