Like on Instagram and Twitter, when you go to type in the @ symbol on TikTok, a few accounts pop up. The top accounts seem to be the ones you engage with the most. Whether you’re viewing their content or replying to posts on their account, the platform keeps memory of your interactions. In other words, the more you engage with an account, the more often you’ll see the account’s name pop up when you go to tag someone with the @ symbol.

Source: https://www.distractify.com/p/what-does-your-first-at-mean-on-tiktok