Neither of these situations are 'weird'. The body responds as it has been conditioned to to various stimuli, kinda like Pavlov's dogs.
For the new mother who'd been nursing a few months, that's more than enough time for the body to develop a habit or pattern. The most obvious stimuli is the baby crying. Since newborns need to nurse every 2-3 hours (or more often) around the clock, your body would respond to the cries of the baby to provide milk.
For the times when you were mopping the floor or otherwise not near the baby, I can only guess. 1) The usual nursing time had past for whatever reason and the body responded based on the time interval like waking up every morning at the same time with or without an alarm clock. 2) The breasts hadn't gotten into synch with the baby yet. My wife (mother of 6) often had to deal with this situation until her body got into the regular pattern of letting milk down at the right time and in the right volume. 3) A stray thought crossed your brain to the effect of "It's about time to nurse the baby again." That's enough to get the breasts active. (MOF, that was enough to get us pregnant!)
For the aunt, this is also not that weird since once a woman was pregnant and nursed a baby once, she would then be capable of producing milk for any baby at any time for the rest of her life. In olden days before "baby formula", women could make a living by "wet nursing" the babies of the aristocratic women who didn't have time for such "domestication". It was also important since grandmothers could nurse their grandchildren if their daughter or daughter-in-law died when the babe was still young.
-TNF