It was a free event, for FemSoc and Comedy Society members. Some FemSoc members decided they wanted to no platform KS, but lost the vote, so they decided to tell people they would picket.
The 8 tickets thing is a complete red herring, tickets were being sold to people from outside the 2 societies and the general public, everyone else would just turn up on the day.
The irony is that KS was doing a set on free speech, and she has been no platformed. More and more women are being no platformed for having views that don't fit in with others men even if they aren't there to talk about their "problematic" views. Germaine Greer only just escaped being no platformed in Cambridge last week, probably because she's such a big hitter, but Julie Bindel is regularly not allowed to speak, even if it's about a subject unrelated to trans* issues.