That's really strange, and doesn't sound right to me. If there was anything that happened that caused the car to shut off because of a bad backfire like that, it should have stored codes. I would expect to see something like a 030X misfire code, for instance, or maybe a catalytic code or something like that even. Probably a whole rash of comms error codes as well.
I would recommend doing what I do: I carry an OBDII reader in the car with me at all times. That way, any time anything happens, or even if I just want to check, I can plug it in and read the codes right there, wherever I am. That's something I would recommend to anybody, not just with this car but with any modern car.
But again, I think it's very strange that the Ford techs didn't find any codes. I think it would be very unusual if there were no codes after that situation occurred.
By the way, how often are you driving the car? With the pandemic a lot of folks aren't driving their cars as much. Make sure you don't let gas sit in the tank forever and get stale. I'm not saying that's what happened at all, but just be aware.