@Luis Alejandre: Not missing that point at all !

Your tool didnt give false positives, just didnt report many of the plugins that are being used and of course we are aware that not all plugins are detectable for a variety of reasons - that is the exact point !

Some sites like WPBeginner, as they have said, publish a list of plugins they use and others will respond to polite enquiries asking what are used. Do tools like this do any harm, no of course not, but their limited usability, due to very good reasons, should simply be understood