This strengthens the argument by making it more likely the laptop caused the navigation system’s behavior during the off-course landing.

This strengthens the argument by confirming that cassette players, laptops, and other devices produce radiation. It rules out the possibility that some electronic devices emit no radiation, which would weaken the argument.

This strengthens the argument by ruling out a powerful counterexample. If similar behavior had occurred on flights with no passenger-owned devices, then the laptop’s responsibility would be less likely.

This strengthens the argument by confirming that passengers sit close enough for radiation from their devices to reach navigation systems. If all the passengers sat too far away for their radiation to reach those systems, the argument would falter.

This is irrelevant. The author concludes there’s a risk presently—it doesn’t matter when passenger-owned devices and low-power circuitry became prevalent, so long as they’re both prevalent right now.