As I said on another thread, I don't have photographic memory (hence struggle to learn song lyrics) but do have what I call audiographic memory, I.e. find it much easier to remember tunes, and this also extends to having a fairly close guess at pitch, either in naming a played note or e.g. "Sing a G".
Relative pitch was instilled into me at an early age through the aural tests you had to do for graded piano exams: e.g. Two notes played - what is this interval? Or "sing the note a 4th above this one". There were little tricks to help learn and identify them, such as "my Bonnie Lies Over the Ocean" - first 2 notes = major 6th, "Auld Lang Syne" for perfect 4th.