I don't have a guitar but I can tap on my desk, and that seems to result in random notes. Maybe there's a way to improve the detection so it knows it's a guitar note?
... but is it really worth it in this case? No, because guitar tuner apps are cheap and plentiful, and electric guitar players use an inline tuner rather than a tuner with a microphone. And for tuners with microphones I get annoyed when the tuner doesn't respond so I prefer a tuner that doesn't try to be too smart and filter out too much.
This is really just a cool example of audio signal processing in javascript (or I suppose we call it "HTML5" nowadays)
Sometimes people go out of their way to find flaws with a service - this is one of those times.