wabi, I've been in many discussions about what is or isn't "fly fishing". To me, it's something that each person has to decide for themselves, as long as they're within the law if it applies. Just as an example, here in MD there are fly fishing only trout streams & "fly fishing" is defined by the law. Otherwise it could be open to interpretation.
I pretty much follow what theboz has posted, fishing with bait is bait fishing regardless of tackle used. Fly fishing is also lure fishing, except the casting method & tackle type differs between a lure & a fly. Of course, a fly can be used with other tackle, but requires something added to provide enough weight for casting, most of the time. There could be exceptions, and there is a bit of overlap especially if you compare ultra light spinning lures & some fly types. In this case, I follow the definition as the State of MD defines it, as it cannot be cast "from the reel" which is what is done with spinning & baitcasting tackle.
IMO the use of pork rind could be debated since it's nothing more than the preserved skin of an animal, something used extensively in fly tying. Adding a pork strip for additional attraction could also be interpreted as the same as adding any other material to a fly in the field to make it more attractive, or to add weight. If you add a piece of rabbit strip to a fly is that not the same as adding a piece of pork rind?
A pork "chunk" might be a different story since there is still fat attached to the skin, so that could be considered bait. But pork rind is preserved with a brine (salt) solution, so I doubt it added much in the way of scent particularly if that 300 lb fish was caught in saltwater. Adding fish oil or juice IMO is the same as adding bait.
Even among those who only use "flies" there is much debate, since a "fly" is a specific group of insects, and does not include all insects as they are designated by science. Same with the many patterns that imitate other things, such as baitfish, shrimp, crabs or crayfish. A baitfish, or any of the others are not a fly, so how can a "fly" imitate a baitfish. It's gets into splitting hairs real fast.
Fly fishing is meant to challenge us both mentally and physically and to stimulate us to figure it out.
Boz, I'm not picking on you, but this is another idea that does not have to define just fly fishing. A person who fishes with other tackle could certainly have the same attitude & thought about the use of that type of tackle.
Fly tackle evolved as simply a means to hold the line & cast an artificial imitation a longer distance. This was before spinning & spin casting tackle. If there was any spiritual implications to the method, then they were just adopted by individuals, just as they are today.
If a person wishes to define fly fishing as a spiritual experience for them, that's fine, but again, others who do not fly fish, and fish with other tackle could feel the same about their preferred method.
Frankly, it's all fishing, and not everyone who uses a fly rod shares that opinion!
If you search the roots of "fly fishing", and go back to a time when it was about the only form of angling with lures or flies, you will find that there have been many things accepted as "fly fishing". At one time spinners added to the tippet ahead of the fly was a popular method as was the use of baits.
To each his own!