How does TikTok know when I’m on my “secret account”

This is so random lol but I'm just wondering how the algorithm knows when I'm on my "secret" account. I have a second account where I follow a lot of people (I just don't like to have my main account flooded so much) and I don't get on it very often but I signed in today and the first two things that popped up on my FYP were basically like "Hey person scrolling on their secret account!" How do they know??