>It's not clear why TikTok is singled out here, this could just has easily been posted to Facebook or Instagram or one of the other myriad of social media platforms, or pushed automatically to someone's open photo album in the cloud.
There's an additional layer here that's often ignored: that specific piece of information that leaked is the same regardless of what platform it was released on, but if it was released on a foreign government controlled platform, that government might start monitoring aspects of data being collected by TikTok that aren't being posted for the user or look at historical data if it's being collected. More detailed location data, who their friends are, where they typically go, and so on. Not all of that additional data is probably going to be available to them on Facebook, just the video. The information in the video may be more valuable when it's incorporated with a series of other data points that may be attainable from TikTok for that now closely monitored account.
Sharing this information to begin with isn't good but it's even worse if you're now potentially leaking additional data unknowingly. Maybe the guy who recorded that begins taking photos at some specific base, maybe their TikTok friends include some coworkers that include some videos in on a boat in the South China Sea... it's possible to start linking more information together that could be valuable to an adversary.