Let's first look at what happens in the text.
So Montag meets Clarisse and marvels why she isn't in school, as she should be.
"Oh well, they don’t miss me. I’m antisocial they say. I don’t mix. It’s so strange. I’m very social indeed. It depends on what you mean by social, doesn’t it? I mean, social to me means you talk to people about things.” she replies. "Being with people is nice, but I don’t think it’s social to get a bunch of people together and then not let them talk, do you?"
We then find out how her classes look like: watching TV, then sports, then transcription history and then more sports. Asking questions or having intellectual conversations is not the done thing; instead, the pupils seem to be learning mostly by mindlessly memorising facts:
"They just run the answers at ya, bing, bing, bing, and us sitting there for four hours of film teacher. That’s not social to me at all. It’s like a bunch of funnels and a lot of water poured down the spout and out the bottom and them telling us it’s wine when we all know it’s not. They run us so ragged that by the end of the day, we can’t do anything but go to bed or head to a fun park to bully people around…”
In other words, she is living in a dystopian world where intellectual pursuit is a crime and she knows it. She is intelligent enough to realise that what she is doing at school is neither learning nor socialisation; as a pupil, she is not supposed to interact meaningfully with teachers and other students. She sees no value in the mindless and hypocritical practices of 'learning' with no thinking involved and 'spending time together' with no meaningful discussions involved; hence her water funnels analogy: pretending that what she does at school is either 'learning' or 'socialising' is like pretending water is wine. It is because she sees the dystopian society's hypocrisy for what it is that she is deemed antisocial. (Compare with Mildred, who is entirely apathetic, but perfectly integrated in society).