They might not know know, but there sure can be a lot of meta data one can use to determine that a person goes to school, where it might be, and what school it most likely is.
Or someone else straight up posted the information publicly. That’s always a possibility you have to consider.
Either way, isolating certain websites and services from each other and/or the rest is certainly a good practice to limit what they can gather about you. If you don’t do that already, that is.