Yeah I thought it strange too. First time I have seen that. I did a walkabout outside, even though I was just there looking for iron in chests, and saw blueberries, wood & medium leather on the ground. Took me a second to figure out what it was, the I realized it was material for a blue&white striped banner I had attached to the chimney. It is possible my base was not attacked by a drake intentionally, it could have been collateral damage from its engagement with a golem, in the vicinity of my cabin.