It doesn't necessarily mean it's directly based on one's own engagement. I don't use tiktok, but on Instagram i mostly follow sports stuff related to what I enjoy (skiing, cycling, running). What content will instagram show me? The most viral content in those categories. What's the most viral content in those categories? A girl skiing in her bikini, a female cyclist with unzipped top, a runner in mini shorts stretching.
But maybe tiktok is better in this regard, heard much praise about their algorithm.