As I have written above there is still a difference between things which look magical and things which are really magical. The dwarves were really good - but they used solid and not magical arts. Everyone with enough talent could have learned it - but the dwarves just had more talent than humen and most elves. Therefore it seemed magical.
But the elves were able to use some kind of magic (glowing blades when orcs are near) and those things weren't learnable. The dwarves weren't able to such things, simple because they weren't elves. But very talented elves are able to learn all of the dwarven techniques. (but there were way more talented dwarves than elves^^)
Gnomi, I think we are probably saying similar things with different words
What is generally known as 'Magic' or 'magical' should be rightly considered as an exclusive/natural Art or Knowledge, and, if we talk about the Elves, absolutely not replicable by the other races; but, as I wrote above, it's very unlikely that the Elves consider themselves or their artefacts really 'infused' by Magic, as an additional quality which comes out of nowhere.
The Elves 'just' regard their creations and power as a 'natural' Knowledge/Art of theirs, which is not replicable by the other races, because this kind of Knowledge refers and is ineluctably bound to their own nature.
The Elves thus know how to make swords shine in specific conditions as a 'common' Art/Knowledge of theirs, just like Yavanna knows how to raise enormous and enlightening Trees from the ground by chanting, or like Varda knows how to craft Stars
The Dwarves and the Humans too have their own proper and specific Arts, but they obviously lack the 'magical' characteristics of the Elven ones, and can be learnt as well by the Elves themselves, because the Elves were the first ones to awaken as fully sentient beings in the World, and were endowed with much more Gifts.
Then, said these things, I never wrote that the Dwarves can use as well the Elven Magic/Arts, or that they can defy the physical laws of the World.
I wrote that they, as a specific race with a specific nature, surely possess secret and specific Arts (their natural Arts), which would easily be able to craft advanced machines or engineering systems; so much advanced to be regarded as 'magical' or impossible by mainly Humans (as we all are
), as a mostly scientific and strictly rational approach is exactly one of their (our) characteristics
It's not really crucial focusing strictly on this PJ's interpretation, since the topic could certainly involve any type of other 'advanced' machines.
The significant point is that the Dwarves can surely count on unknown and ancient Arts and technics, which make the creation of anti-arrows nets (or other numerous things) easily possible.
I admit, though, that I would have never imagined that a scene of very few seconds, concerning ballistas, could have created a so deep and interesting debate about the very foundations of the Tolkien's Legendarium
