I don't think you're understanding what the person you're replying to is saying.
If the app is made by an adversary, you don't need to post it publicly for there to be a problem. The app has the ability to send it directly without you even knowing.
By "Solve the problem of people posting this to social media" I mean the more general "you shouldn't be accessing apps that are security problems while in a secure area, which I covered in a separate thread on this article.
In that respect, whether it's TikTok or any other social media makes little difference. If it's use of apps like that is prohibited, then it's either not a problem or it's a personnel following policy problem.
That said, if people really think TikTok is a problem they should be worried about some other app that's ties are far less known that might get far less public scrutiny and do far more. By the time we're nitpicking which specific social media platform is the worst to have posted to in this case, we're so far down the path of problematic behavior that we're in absurdist territory. The fact that someone's walking around with the equivalent of a video camera taking movies of what appears to be top secret material is the problem, and whether they put it up on TikTok or YouTube, or sell to the Washington Post or to RT is just bikeshedding mostly irrelevant details.
The solution to this all is probably along the lines of "don't allow smartphones in secure areas" or only allow smartphones that have been vetted by security.
If the app is made by an adversary, you don't need to post it publicly for there to be a problem. The app has the ability to send it directly without you even knowing.