It is very odd, as I have never installed the app or even googled the term. I have seen some as linked Instagram feeds, but involuntary. Tiktok would be the last thing in the world I care about, I am also quite a bit beyond that age bracket. Usually it's a woman doing a poorly choreographed dance move or two while displaying a duck face. I am not sure if that is possible but maybe somehow there is an IG/tiktok data exchange if someone has an account on both. This still happens even though I have terminated the ig and fb accounts a while ago