Heya! I've actually had the exact same thing happen to me, word for word.
I applied before deadline for illustration at Brighton, was given a conditional offer and asked for my portfolio, and was then told that my portfolio was a better match with content creation a few days ago- about a month after sending my portfolio in (also recieved the unibuddy invite and postcard between submitting my portfolio and recieving their decision.) I also firmed my offer early.
The content creation course is new for this year, so i've been wondering if perhaps they gave out their capacity of Illustration offers and are trying to fill up the new course with the remaining applicants?
So sorry to hear that you've been having to deal with this too- I know that it's left me feeling really down since I got the email. Please try not to let their decision make you feel like your work isn't good enough- i wish you all the best in your applications, and I'm sure you'll find a great place 👍😊