Whether a fight is griefing or not is obviously a matter of opinion. That opinion can be partly based on fact, though a 'losing' player, the self-perceived victim in the fight, often won't know all the facts: were they attacked or killed by a player using an exploit or cheat, was the attack made for fun or just because they were an easy target, or with the intention of causing grief to the victim, rather than for gain. From a single incident, there's enough ambiguity that the facts often won't come out. If there's a sustained pattern of behaviour that someone (probably someone at CIG, less likely players) can see, maybe the fact of the cheating or griefing can be found out. I think there are sometimes apologists for griefers who hide behind the "they might have been trying to steal your stuff" excuse for just murdering and blowing stuff up, because who knows for sure what the intention was.
But a large part of anyone's opinion about whether a fight was griefing or not is purely subjective, not based on any fact however known or unknowable. Should the victim have anticipated that other players might attack them or their ship in that location, perhaps given what they brought there and were doing there? If they should have and didn't, that's on them - if they feel victimised, that's their opinion but not necessarily right. Great examples above - in lawless areas like Pyro, anything goes, and the rewards available there are intended to compensate those who dare take on the risks and come prepared to win a fight or to spot the danger in time to turn and run - great! It's fairly clearly communicated and if you're paying attention you should be able to spot the danger, or have a plan to deal with being ambushed - not having all your wealth and possessions on you at once, being able to run away. A player around outside Port Tressler for a couple of hours, firing at every industrial ship that approaches, when the comm-link is up and still somehow no UEE vessels are showing up to get rid of them is probably griefing; the players doing industrial stuff should reasonably expect the game systems to provide some protection from that.
It's important that the game's design and the way CIG and the game itself communicate the level of risk to players, and game systems back that up with some protection in 'safe' areas, and less or none in 'lawless' areas. A lot of this is in place already with the comm-link satellite status indicators, Pyro's reputation, station defences (when they work) and a crime stat system (when it works). The station defences don't always work properly, it seems, and I'm surprised some of the crime system is so janky, but the foundations are in game already.
Discovering new and interesting ways to use the toys in our sandbox in an attack, in a lawless system, one time doesn't seem like griefing to me. I think the burning shield generator and fire mechanics might need some adjusting if they become a problem when used that way. Just like regular doors, it should take some effort - some firing - to get through an air shield and into a ship owned by someone not in your party, but it shouldn't be impossible. But for every time a game mechanic needs tweaking (the air shield that lets anyone in, the shield gen that can act as an incendiary) there's also a case to make that players in Pyro should expect saboteurs if they aren't crewing their large ships, watching and defending the entrances, and not fighting intruders while using fire extinguishers. Parked up 10km from New Babbage? You probably shouldn't expect that sort of attack to come without the cavalry arriving to help you.