> Instead, Threads’ boost in daily mobile usage may be driven by other factors, including cross-promotions from Meta’s larger social apps like Facebook and Instagram (where Threads is regularly advertised to existing users)

This. I use Instagram and every time I scroll through the feed there's a stripe of Threads content, clearly algorithmically chosen to grab attention. The thing is, only the top part of every post is visible, and one needs to download / go to Threads to read the rest and the replies (many posts I've seen are specifically the kind where you're more interested in replies than the post itself).