I don't think the word "flagship" is the issue. The issue is that no other noun follows. If this was "flagship factory" or "flagship truck" it would be much clearer. To me the headline wasn't clearer do to "flagship" being followed by "socked" which I am most commonly used to seeing as a noun rather than a verb, especially in a news article rather than a conversation in a pub.
As a Car Guy, when they said 'battery flagship', I immediately understood that to mean the F150 Lightning: the top-of-the range version of their most popular vehicle, which also (now) runs on batteries. (The Lightning used to just be an obnoxiously-fast V8 truck.) Therefore: "Ford's F150 Lightning is moldy." Ew, nasty!
Finding out that the author didn't intend "flagship" mean the truck, but a factory, is baffling.
It's not normal usage at all, as it's missing the main "thing" that is the flagship. Flagship What?? Imagine it applying to any other thing to see what we mean.