They can do this through Apps
visits through websites
zillions of ways to accomplish this
nothing is secret or secured if it on the web
But the Chinese probably won’t find my grocery list all that interesting
Unless they think bread, milk, eggs are secret code for nuclear weapons haha
Why would you need to write such common things down?
You wouldn't.
And then to mention it on the net - is a communication.
Combined with your mysterious alphanumeric username, it's easily a code.
Expect a visit... comrade...