It's never made clear, as far as I am aware; but there is an implication that many or all elven artefacts contain some level of what we would call 'magic', and that they respond to some extent to their bearer's need and desire.
The elven rope that Sam carried after they left the Fellowship seemed to 'come when called', holding firm as long as they needed it, then unfastening itself when Sam 'called' it; yet it was not called out as having any unusual virtue.
"What are these?" asked Sam, handling one that lay upon the greensward.
"Ropes indeed!" answered an Elf from the boats. "Never travel far without a rope! and one that is long and strong and light. Such are these. They may be a help in many needs."
"You don't need to tell me that!" said Sam. "I came without any, and I've been worried ever since. But I was wondering what these were made of, knowing a bit about rope-making: it's in the family as you might say."
"They are made of hithlain," said the Elf, "but there is no time now to instruct you in the art of their making. Had we known that this craft delighted you, we could have taught you much."
The elven boats were also not seen as particularly enchanted or modified, yet they, too, apparently had some unusual virtue of their own. The funeral boat, for example, was cast off from Parth Galen and sent over a waterfall, but...
in Gondor in after-days it long was said that the elven-boat rode the falls and the foaming pool, and bore him down through Osgiliath, and past the many mouths of Anduin, out into the Great Sea at night under the stars.
The boat was also seen by Faramir; it could have been a vision, but if so it's not explicit. The implication does seem to be that the boat knew the will of its masters, and carried its last cargo in honour.
There is also the case of the beryl-stone, left on the bridge on the road to Rivendell. It sat there for two days unmolested by other travelers or even wild animals, at a time when the Nazgûl were about, and served as a sign to Aragorn that the bridge was safe to cross.
None of these artefacts were called out as being especially magical or having any unusual powers, yet they do seem to establish a pattern - Elven-work seems rather good at following its bearer's wishes.
The brooch was left behind by Pippin as a sign that he, at least, was with the orc party, still alive and still hoping for rescue. It served that purpose, which seems to put it in the same category as other elven artefacts.
So, was it deliberately enchanted? No. But was it magical? By our standards, I would say 'probably'.