From the article:

When we asked them about editing out the pins worn by Leicester’s University Challenge team, a BBC spokesperson said: “In line with our editorial guidelines, we advise that no badges, flags, and emblems or symbols are worn or visible during filming, along with clothing with obvious branding or slogans. If such items are not removed for any reason then a decision is made between the programme makers and the BBC regarding any edits to the programme.”

But the article doesn't say if this was made clear to the participants before they agreed to participate. The reaction of the students suggests that it was not made clear in advance.

Another perspective: this is how Ireland’s national chat show handled an unplanned display of Palestinian emblems (skip to 1min 30sec) https://inv.nadeko.net/watch?v=f5pgd1Ab53I