Running pre-imported top level packages like "runpy" or "site" with "-m" is supported behaviour, so that shouldn't emit a warning. ("python -m site" in particular is a debugging tool used to print out the default sys.path configuration)

Otherwise, the warning mostly looks good to me, except I'd suggest either dropping the word "any" from "any parent packages", or else replacing it with the word "all" (since the key point to be conveyed is that by the time the module starts executing and this check is made, all the parent packages have already been imported, thus triggering their side effects, if any).