I always read the subtext as "This installer will run a script whose stated goal is to determine if the package can be installed, but y'know, it's a script, and its existence is warranted for doing supposedly helpful yet nonstandard checks that the pkg API-or-something doesn't provide, thus can't be sandboxed, and therefore can do anything else it wants to. Would you like to assume trust and proceed anyway, or would you rather cancel and possibly audit the thing beforehand?".

But that's my paranoid tech background speaking. I can totally understand technical naïveté though.