I'd say it's very possible for intense but ordinary life pressures to put people into a variety of the Progress of Insight states. I was bullied in middle and high school, and in retrospect a lot of the mental states I went through as I tried to figure out what to do and what it all meant about me as a person were kind of classic Dark Night/A&P states. For example, I'd been a lifelong agnostic despite attending Catholic parochial school. But then one night it suddenly made perfect sense that God was real, I needed to convert to Catholicism, and everything was completely fine. And then that certainty and peace evaporated over the next couple of days and my existential crisis returned. Later on in life I'm pretty sure that the end of some romantic relationships also triggered some classic Progress of Insight cycling.
Meditation is only one approach to getting the mind to heavily scrutinize our sense of self and how it relates to other people and the world. Heavy scrutiny causes synchronized neurochemical changes that cause the manifestation of Progress of Insight stages. Shifts in life circumstances can produce the same intense pressure/pull to scrutinize that relationship to other people and the world, and therefore the same PoI stages. They may not occur with the same clarity or effects or sequence that heavy meditation would cause though.
It's also worth keeping in mind that an interest in spirituality and reading MCTB or this forum is also indicative of having possibly crossed the A&P in your past, even if not recently.
Is it possible to cross the AP and be in a Dark Knight state only by doing shamatha (fire kasina)?
Absolutely yes.
