The car was a Chevy Malibu, 1978 or 79. If it has the original drivetrain the timing is adjustable, and if the car was out of tune or the carburetor hasn’t been overhauled after all these years, it could be very well be prone to backfiring.
I started driving in the 1960’s. The only way to get an automobile to “backfire” on que, is to intentionally turn the key off for a few seconds than back on. The vehicle needs to be in gear and moving. Cars made prior to column locks were easy. Once column locks began, it is increasingly difficult. Automatics forget it. Rarely does any vehicle manufactured since WWII backfire just driving down the street.
Of course for those us who know what distributor (relic) timing is and how finicky the jets/adjustments on a carburetor can be, entirely possible...not to mention a bad coil or spark plug wires shorting.
We had a ‘72 Malibu. One backfire in ‘81. It was back in the day when companies would pay to have vehicles shipped when relocating. It took several months and the backfire happened when we first started driving it after 6 months of sitting wherever it was stored. A few tweaks, it was fine.
We sold it in ‘85 and new owner was still driving it in ‘95. Best car ever. Had we known how it compared to cars manufactured later, we would never have parted with it. After a few more GM cars we went Ford and Honda.
In 1977 a friend bought a ‘75 Chevy. Thing ran like crap. He fiddled with the carb but it really came to life when I advanced the timing. Ran like a rabbit with my best beagle on its tail.
It would sound like someone firing a shotgun when he let off the gas.
And it was an automatic.