Dang, I've never heard of that before. That would be a PITA and I'd be pizzed. My Dad had a huge willow tree removed, the guy chunking it hit heavy duty roller chain in a crotch about 15 feet up. I hit a ceramic insulator once and a cinder bock in another.Years ago my uncle had a huge maple in front of his house-don't remember why-but it had to come down. Tree service took it down from the top, when they got to the trunk several feet up from the ground, they hit something that destroyed their chains. Long story short, apparently the tree developed a hollow years ago, and a former homeowner filled it with concrete. Ouch!
I found something in my stove the other morning. I was raking coals and heard a clang of metal on metal. Apparently when I was splitting some Hickory I must have gotten mad and called it a day after getting a wedge stuck in the wood. I must have forgotten about the wedge being stuck because the next time I went out to split wood and split that piece down to a small enough chunk leaving the wedge hidden. The night before I was loading the stove and distinctly remember saying to myself "this piece is heavy it will burn like iron". It definitely burned and left the iron glowing cherry red among the colas for the morning.
When you find stuff in wood; I can tell you from first hand experience, it was most likely left there by a moron!!
Sorry about your chain.