Which means the MP said something that caused the Mac, iPhone, Apple Watch to think the "trigger" phrase was spoken. It did not listen and send things to Apple Siri servers and decide to enter into a political debate.
False triggers can happen. Computers are far from perfect. For that matter, someone sitting nearby could have said something that caused Siri to trigger.
I am just saying that without the trigger phrase (or something that the device things is the trigger phrase), nothing is being sent to Apple Siri servers.
NOTE: I have Siri disabled on my Mac. I have speak to trigger disabled on my iPhone. But I do have Raise to speak and "Hey Siri" enabled on my Apple Watch. Once in awhile, I will raise my Apple Watch and it will hear something it thinks is "Hey Siri" and attempt to answer a question. But since I am not in Parliament, this is not a news (or humorous) worthy story for the Guardian.