They were telling users who to blame and who to thank because in this specific case, the blame and the thank are pretty clear. The Biden administration approved the ban, and the Trump administration reversed it. Blaming one and thanking the other is also hardly surprising.
There is no question that TikTok is a politically sensitive app and the US/China are very nearly in the funnel to a major war so a lot of the usual niceties are questionable. Previously the US has attempted something that looked a lot like a black-bag kidnapping of a Chinese industrialist [0]. I'd imagine that the TikTok people are acutely sensitive towards how the law is actually going to be interpreted and enforced in practice.
Jan 17: Biden administration says it will leave TikTok ban enforcement for Trump [1]
Early Jan 18: Trump says he will 'most likely' give TikTok a 90-day extension to avoid a ban [2]
Late Jan 18: TikTok makes app unavailable for U.S. users ahead of ban [3]
Midday Jan 19: TikTok begins restoring service for U.S. users after Trump comments [4]
They already knew what was going to happen. They also changed the message shortly after disabling it from "We're working to restore service in the U.S. as soon as possible, and we appreciate your support. Please stay tuned." to "We are fortunate that President Trump has indicated he will work with us on a solution to reinstate TikTok once he takes office. Stay tuned!" [5]
[1] https://www.nbcnews.com/politics/joe-biden/biden-administrat...
[2] https://nbcnews.com/politics/donald-trump/trump-likely-give-...
[3] https://www.nbcnews.com/tech/tech-news/tiktok-makes-app-unav...
[4] https://www.nbcnews.com/tech/tech-news/tiktok-says-restoring...
[5] https://www.nbcchicago.com/news/tiktok-sends-notice-to-users...