Man, the conspiracy theories here would make The Donald blush...
OEM tires are just the tires some engineer and his bean-counter overlords agreed would work and meets the financial targets for a specific model. Some times it's a standard spec tire, some times it's a tire designed specifically for that model. It's not uncommon to see tires that are sold in the aftermarket also have a bike specific version. They are similar but not the same, and unfortunately, it's not always obvious from looking at the commonly published info, what the differences are.
Kawasaki has often used "special" Dunlop tires for its lower end bikes. As Wal mentioned, the differences seem to be they are often a single compound vs. multi-compound similar tires available from Dunlop. In Dunlop's case, they are typically labeled with a different model number in that tire family. Other brands often denote the difference with a model specific letter at the end of the name. But if it says Dunlop, Bridgestone, etc. on it, it's a tire made, tested and guaranteed by that manufacturer and it's exactly what the bike manufacturer spec'ed and ordered.