Looks like you are pretty close. And it appears it wasn't a "Chinese part" so much as Chinese alloy provided by a contractor to manufacture a magnet. It seems pretty strict that even raw materials such as this alloy cannot be sourced from China. Considering Russia's struggles to build advanced weapons with all the current sanctions, a wise move. From a more detailed story:
Honeywell International Inc., an F-35 subcontractor, notified Lockheed in late August that “alloy sourced from the People’s Republic of China” and provided by a “fifth-tier” subcontractor was used in a magnet, Laura Siebert, a spokeswoman for Bethesda, Maryland-based Lockheed, said in a statement.
Here’s the reasoning for not using foreign sourced materials. Building a weapon system requires a complete infrastructure. Here’s an analogy. You want to have a healthy population of Florida Indigo snakes. But having the snakes requires large areas of a particular type of land with the right type of food source. The snakes are almost extinct because their habitat has been taken over by lots of subdivisions with neatly mown lawns and all the swampy areas neatly piped into French drains. There is no longer an ecological space where the snakes can survive.
The same thing is true of alloys. The manufacturer requires an ecological niche where he can survive. This means that someone has to buy enough of his products at a sufficient price, so he not only survives but thrives. The more money he makes and the more desired his products are the more sophisticated he can make his processes and the cheaper and more available the material becomes.
One reason why China has cornered the “rare Earth” metals market is because the processes needed to purify them are ecologically damaging. Think lots of acid washes. So, the various state and federal EPAs have shut down the American mines and processing plants. This is very damaging to national security. Trump husbanded a California mine and processor to the point where they could get back into production. I can’t find anything on the project, and it wasn’t certified before he left office. My guess is the EPA shut them down. This is the same thing except the mine isn’t directly connected to a high priority project.