I did not study CompSci but microengineering (mix of things, including robotics and manufacturing) and I am now working there as a SRE. Some colleagues are mathematicians. So definitely not only CS background :)
It was frontend. I did ok with some heavy studying, but I'm definitely more UI focused on a day to day basis. The problems I had to figure out during the interview were nothing at all like what I do daily.
I walked away feeling like if I really wanted to I could knuckle down and study for longer and get a job there, but I decided it wasn't really my thing and went in other directions. Like I said, I took the studying and the subject matter as a challenge and I feel pretty pleased with how far I got considering I have a painting degree.