Those things aren’t mutually exclusive. Yes, they are dumping massive resources into SMIC. Yes, they also want to maintain imperialism over Taiwan, and TSMC is a part of that. Some of it is fear-mongering sure, but China is consistently confrontational in the South China Sea and beyond. There’s a reason they enforce an abrasive naval presence there and continue to press against the Philippines.
https://www.ft.com/content/b4ee2e18-3256-4371-8369-9a3118959fca
“Uh, it just happened to fall on it. In any case, here’s gravity”