Well, if it happens with the guitar and only the guitar and you can do that at any time. You have a pretty good relative pitch. If it's only that one time, then call it the luck of the draw.

Perfect pitch can be useful if you're a trained musician and reallly know what you're doing when it comes to composition. But I'm not and I don't. Don't let me sound like I know what I'm talking about because this is all I know about the subject, but where as usual notation of music only recognizes the 12 notes, Indian music recognizes all of the semitones between notes, you can throw as many notes into an octave as you wish. These semitones are only achieved on traditional stringed instruments by bending the strings or detuning while playing. But they can also be played on trombones, theremins, analog synths by tweakings the fine knob, anything where the pitch works on a slide.
I think semitones can make music sound much more well defined and customized.

Just to clarify, the twele tones are made up from semitones, so the other notes I think would be demitones... possibly...

But I think these notes are used in a few eastern musical styles. I'm no expert though.

microtones

Are you sure about that?
I though you'd use microtone to describe almost inaudible differences in pitch...

nope, microtones are anything smaller than a semitone.

Cool, thanks for clearing that up.

So how would you notate microtones?

i took out a book on microtonal notation... it's pretty much different for every composer. some of them use weird sharps and flats that only go up a quarter tone or however much

What instruments generally play microtones?

it's question after question!