[Tor3]

That's simple pitch memory. I started playing guitar at 12 and at that time used a tuning fork - and I noticed that after a while I could hear the "right" note of the A string in my head and I didn't really need the fork anymore. That ability is just pitch memory (which can be thrown off) combined with learning the timbre of the instrument you play (in my case a guitar string).

And yes, that's not the same as perfect pitch, which typically includes much more than the above. I certainly don't have it, even if I can pick any string first time in the morning and hear if it's "off". Because that's all I can do. But then again I don't get annoyed by "out of tune" sounds in the world around me, unlike what people with perfect pitch sometimes tell about.