I wonder how many of these users are unique. TikTok makes it simple to have two or more accounts. A number of content creators (especially ones who make NSFW non-nude content) have alt accounts that they can use when their main gets muted.
Something that definitely can be done in TikTok also but the nature of the content (video) make it more complicated.
FB is full of people with double profile also, I've friends that have been having two profiles for ages. I think is a common issue
Instagram despite being around for much longer and not being banned in the largest internet market (India) has only 1B MAU.
Tiktok isn't available in China either. That's a different app from bytedance if I understand it correctly