Just like Reddit and HN? This is not a news for many.
> Notably, he claims that ByteDance engineers stole popular content from apps like Instagram and Snapchat and put the videos onto TikTok
Also not a news but there is always a question of who really owns the content. And it's not the ones who originally made it, that's for sure.
Following copyright law (and common EULAs) it would be the ones who originally made it, with a perpetual 'do whatever you want' license granted to the platform. Without a DMCA takedown request it's not going to be enforced automatically though. The main issue here at least for US law is now that TikTok employees have posted content they are a publisher which could lose them immunity from DMCA lawsuits against user submitted content. Additionally on the ethics side, generally it's assumed that another user is stealing/reposting the content, for a platform it's less acceptable given that it would purely be for financial profit (which the original creator is not compensated for)