This is most likely because her parents/grandparents changed to using patronymical last names, precisely to avoid this problem. There was a very popular movement in South India (particularly the state of TamilNadu), called the self-respect movement, which a large part of society (except for the upper castes - who had a lot to lose), adopted.
This is why my own name does not give away my caste. Because my grandfather switched to patronymics from the existing caste based last names.
(In Telangana, surnames are almost exclusively used as just an initial preceding the given name, and sometimes that’s even all that ends up on official documentation.)
What happens of they find out you’re a lower caste, so they just stop talking to you, talk down to you, etc.?
I'm also not lower caste (or particularly upper caste for that matter) and my parents were doctors, so my family was relatively well-off in a very, very poor part of India, so almost all other social indicators would tell them to place me higher in social status. So, the experience of others would vary.
I am someone who was not given a caste-based last name because my parents were influenced by a regional movement against caste. (I didn't even have a last name to begin with but eventually added a non caste-based one to avoid visa issues.) Whenever I traveled by train and chatted up with a co-passenger, almost surely they would ask my name and would never be satisfied with just knowing my first name. They would get visibly confused when I would tell them I didn't have a last name.
Edit: Curiously, based on the last name of the person (Soundarajan) whose talk got cancelled, I would actually have guessed that they were upper caste (Brahmin - the highest).