> it's a stretch to assume the students did anything other
No, because at least one (edit: two!) incidents like this has already repeatedly happened elsewhere. Chinese students sabotaged a panel at Brandeis University about Uyghurs ("Viewers interrupted a Harvard-educated lawyer as she tried to describe her brother’s plight in a concentration camp, scrawling “bullshit” and “fake news” over his face on the screen and blaring China’s national anthem." - which is pretty clearly harassment), and an Emerson College student was subjected to doxxing and death threats[2]. Given these incidents, and that the university president released a letter about this (so it's not just an unverified social media post), the reasonable assumption is that the students did engage in harassment.
Moreover, yes, students in a foreign country reporting an incident legal in that country to their repressive home government is definitely "collusion".
> Freedom of speech in west =/= freedom from consequences
Um, no, that's incorrect. "Freedom of speech" means that you have the ability to express the opinions that you want to without consequences, by definition (the two components of freedom of speech are the ability to express opinions and the protection from "consequences" (which is a misleading way to say "active retribution") of that expression).
In the United States incarnation, the First Amendment is a specific instance of a law protecting freedom of speech that prevents the federal government from punishing you from saying what you want, modulo a few edge cases (most of which aren't restrictions on freedom of speech/expression so much as restrictions on particular utterances (e.g. yelling "fire" in a crowded theater) or knowledge (disseminating classified information)).
But, beyond the government (which is the only entity that the First Amendment applies to), other organizations or individuals can take pro-free-speech or anti-free-speech positions, which (again) means freedom from consequences due to that speech.
The CCP here is clearly taking an anti-free-speech position by threatening the student through his parents due to an opinion that he has expressed about Tianamen Square.
> Rich Chinese kids with social media are playing the same cancel culture game
Also completely false. "Cancel culture" means that you're attacked by the culture specifically, which includes just about everything except the government.
[1] https://www.propublica.org/article/even-on-us-campuses-china...
[2] https://news.ycombinator.com/item?id=29593320