Yes, having more people involved means a greater chance of someone simply talking to the police, but the same applies to a single person you had a conversation with in your bedroom. You do not have any legal protection against a person you talked to telling the police/government what you said (with the exception of _very_ specific set of explicitly enumerated cases), regardless of how many people were present.
But we are not talking about people voluntarily talking to the police, we're talking about secret police surveillance of a private group. What the police were asking is "can we put bugs in a private clubroom/union hall/church without a warrant?".
Also, including what china did in HK in a conversation about rule of law, human rights, etc is simply not relevant by _any_ definition.
It is , but in another way - we are finding there is little daylight between us and China in terms of surveillance.