We call this phenomenon "quantum learning." Don't know if that is the right term for it or not, but there is no other emotionally resonant way to describe just how shocking/jarring the phenomenon is.
She has always been like this. It's how she learned to walk, to talk, to ride a bicycle, tie, her shoes, to read, etc. etc.
DS3.5 has passed through enough milestones that I'm starting to think his path is something similar, but with a warning tell. It's usually an early and short-lived manifestation of a new skill, followed by a seemingly fallow period of internal stealth testing with no apparent outward progress, then full (?) proficiency revealed. It's like he's excited at the idea of a new skill/interest and experiences emotional leakages of enthusiasm, but he wants to perfect "it" in his head before the big reveal.
YES.
DD did have that kind of "tell" with early motor (and verbal) milestones. You'd see a behavior only once-- and then not again for weeks/months. If you
asked to see it again-- she'd PLAY with you. (Maddening, that.)
She held her head up unaided at delivery, for example. She rolled herself over (unaided, again) when she was less than 4 days old. We actually have the former on videotape, along with the gasps of disbelief from physicians and nurses alike. She didn't do either thing again for weeks and weeks. I mean, she was reliable with those milestones WAY ahead of schedule-- just not freakishly so the way that we
knew she actually was (because we'd seen her do it deliberately at least one time).
She also tended to see
consequences for her own actions (or those of others, more strangely) at ages that
still boggle my mind. She didn't stand supported (other than with another human being) until she was about eight months old-- but then again, she had already worked out how to get back into a sitting position without tears, too. She definitely had the dexterity-- she was doing it with a person holding onto her hands by the time she was about five months.
She's always been a kid that wants an exit strategy. LOL.
She was
definitely talking some by 6mo, and understood a truly awe-inspiring amount of OUR language at that age.
Demonstration of any of that, on the other hand, was
never on demand. In fact, she almost seemed to take perverse glee in
denying you what you asked for.

Extrinsic motivation (or competitive motivation, for that matter, outside of a VERY few circumstances) is a nonstarter with my child. Period, full stop. She does stuff her way and in her time-- or not at all. Her nickname in daycare at 13-15mo was Little Ghandi. She was deceptively rational and easy to get along with-- but if your agenda and hers were at cross-purposes-- WATCH OUT. She wasn't a tantrum-pitching kind of child, mostly, and she was a keen observer of people. She learned that the path of least resistance was the best route forward
most of the time, and that in any event, passive resistance or civil disobedience was a more efficient strategy than fit-throwing. I'm not entirely sure that people-pleaser is the term, even. It's clearly a manipulative strategy, this business of showing people only what won't surprise them unless it is
necessary to do something else.
Until I saw DD as a baby and toddler, I seriously thought people that COULD believe in things like the reincarnated Lama, etc. had to have a screw loose somewhere. Having seen what some PG kids are like from birth, though-- I get it now. No, I don't think anything supernatural
is the explanation! I just think that kids like this can make people reach for the supernatural as an explanation because it seems just as plausible as the truth of that kind of cognitive horsepower. Kids like this are deep, deep thinkers from birth, and they have a lot of raw material to work with. There's some thing a little alien-seeming about it.