i feel skeptical of the story.
either he left out important chunk of details, or has been ignoring some warnings.

i have experience this so called "blackout" driving ICE car.
& in orde for that to happen, it needs to meet 2 criterias.

1) alternator died
2) battery out of juice

in scenario 1, battery ok, but alternator died.
your car will run fine on battery only, until the battery loses its charge.
prior to that, u'll get battery warning on your dashboard.
unless u said those very old car that dont hav battery health check.

in scenario 2, your battery died, alternator working.
first of all, if your battery in such a bad condition that it will die any died, it should long shown battery warning on dashboard.
lets say battery suddenly kong in the middle of a drive (i experience this before), your alternator will still generate just enough power for your car to keep going.
but u can tell obvious signs.
dashboard bcoms dim, headlights, or eben signal light might not work, radio/console died, speaker sound suddenly on & off then no sound.
in such case, u can still drive provided u keep the speed & rev for alternator.
when u slowdown, engine might likely die, then u wont be able to start bck.

then there's other unlikely scenarios like battery cable bo install properly, it came off mid drive.
or some part of car cabling kena bitten by mouse, then com loose mid drive

bottom line is, it should be a lot more to the story that he convenient left out.

istop will not engage once your battery health drop bellow certain percentage.

like u say, probably some other parts like furl pump kong at that very moment.

btw, outside people help u change mazda battery, they will first attach a temporary battery or power bank, then swap out the battery.
while it works, that's not a proper method for modern car.

modern car battery requires to recalibrate battery health after each battery change.
for mazda, there's no problem of changing it yourself, but bear in mind that after install new battery, u meed to run the calibration to re-enable istop.
check your car manual, it's pretty easy instruction.