There is the law of the U.K. and there is the “spirit of GN” (whatever that is)
So when someone is banned, one has to assume that GN has deemed that , that person has broken one or both of the rules.
I also suspect that they may have received prior warnings about posts - although I don’t know. But banning someone for one post seems a tad excessive.
The law allows freedom of speech except
Legal Limitations and Restrictions:
Hate Speech:
Laws prohibit speech that incites hatred or violence against individuals or groups based on various factors, such as race, religion, or sexual orientation.
Defamation:
Defamatory statements, both libelous (written) and slanderous (spoken), are not protected and can lead to legal action.
Incitement to Violence:
Speech that incites violence or illegal activities is not protected and can have legal consequences.
Public Order:
The Public Order Act 1986 addresses threatening or abusive words or conduct that could cause harassment, alarm, or distress.
Other Restrictions:
Limitations also exist for things like obscenity, pornography, copyright violation, and breaches of privacy.
So given the topic, I suspect that rule about hate speech was broken, but I could be wrong.