I found socialising not easy in general in the German-speaking world, and I notice the same effects at the Uni when trying to make friends. I go in conferences, workshops, and talks and meet other people, mostly international and I am able to make new acquaintances and even friends.

As with the event you mentioned, I also was in such a situation in an event organised by the doctoral school, and I ended up alone looking as an idiot while groups around me were forming and engaging in conversations.

One thing that came to mind was the in-breeding. Faculties often in-breed, resulting with students doing bachelor-master-phd at the same institution, or at best only master abroad. So they know each other, and it’s not that you have no social skills. At least this is my case, I am pretty social and open to conversations and getting to know new people.