In a strict technical sense, you are correct. Anything that encourages individuals to participate in their government is promoting democracy. However, I think it's heavy whitewashing to look at this whole situation and says it's TikTok promoting democracy.
I find it very hard to believe TikTok is doing this being they genuinely want to promote democracy in the US. This threatens to end TikTok's influence over millions of Americans, they have a business/political stake in this. They're encouraging people to contact their representatives, not because it's in the individual's best interest, but because it's in TikTok's best interest. That's why it's manipulative.
Also, I'm of the opinion the foreign-funded propaganda is generally unhealthy for a democracy.
Edit: Just to be clear, I don't really want to ban TikTok. I don't trust TikTok, but I also don't want to increase the federal government's ability to censor what Americans can view. In the process of battling Chinese influence, I don't want the US to become more like China.