The title is misleading, TSA is pretty much strictly an American term for our agency, the Transportation Security Administration. In the UK, they are pretty much are just called Security Officers, I am not sure, but I believe they work for the airport, not the government.
But anyway, the article does bring up a pertinent issue. While there are guidelines regarding liquids and other items that you can and can not bring on the plane, all the "rules" are purposely vague. It is up to the officers at any airport to make a go/no-go decision, and of course, different people, different outcomes. So what might seem fine, might not have been seen, or that person did not see it as a threat, so let it go.
Best to use caution, and be safe, or be prepared to lose it.