Yep, it can mean all that. Though knitting with 2 yarns at once is more often referred to as double stranded knitting. And double knitting doesn't have to have a pattern, you would be knitting a double thickness with both sides have a RS facing.
It's usually fairly obvious which is meant - DK yarn is thinner than worsted and heavier than sport weight, and will be used in patterns only where the yarn needed is given. Double knitting will involve a k1, sl 1 type of pattern and double stranded will say to use 2 yarns at once.