"Public" doesn't mean the company has publicly announced it - just that the information is available to the public. The situation you're describing is very similar to the Boeing situation above. You just happen to be the first person aware of the news, because your job provides you the ability to see a bunch of cars and understand how their quality is trending. Nor is it any different than you buying, say, one of the first Rivans, thinking the QC was horrible, and shorting the stock.
Regardless of when you learned it, the quality of BMW's cars (in this example) became public information when they started selling them to the public.
Now, however, if an internal employee told the technician that BMW had removed all QA checks from their line, and (s)he should expect quality to fall precipitously in the years ahead, that would be different.
Regardless of when you learned it, the quality of BMW's cars (in this example) became public information when they started selling them to the public.
Now, however, if an internal employee told the technician that BMW had removed all QA checks from their line, and (s)he should expect quality to fall precipitously in the years ahead, that would be different.