n2gwtl I don't know the answer to your question, but based on the fact that many apps have this same exact date and time just suggests it's a fallback time that they use if the package manager doesn't know when the app was installed or updated. I noticed this on my phone before, and vaguely remember seeing it on Stock as well, though I could be remembering wrong.
It seems that it's actually 2009-01-01 00:00:00 UTC, and you're seeing this date and time because of your time zone.