Forget the picture. When you say crankcase I hope you don't mean you took the cylinder off and removed the clutch gears and magneto magnet and split the case. If you did and you found purple grease and a Woodruff key then return to sender and buy from a new vendor.
Now I can only assume that by finding any grease (of the purple variety I don't know why but it's probably better than stock) you mean you opened the clutch gear side (right side if siting on bike) and found a Woodruff key. Well it's either a spare part (possible with Chinese quality control, consider yourself lucky it didn't get in the gears and turn them to mush) or its a key that unless you're finding slippage a problem shouldn't be investigated too far. The key is almost arbitrary since the shaft and mating gear is held in place by a taper along with friction pressure via a bolt or nut.
If it's under the clutch gear area pull just the small bevel gear. If the Woodruff key is missing then install it and tighten the bolt back down again, if you have it off I recommend replacing with a hex bolt instead of the flathead screw bolt, it's usually the same thread as the magneto magnet nut.
I recommend to do just the small gear since it turns counter clockwise, without a key it has the potential to loosen the bolt and stop the motor from pulling anything, on the large side the nut is automatically tightening the clutch onto the tapered shaft during use, so it becoming a problem is far less likely.
It's very possible that the Woodruff key is an unexplained mistake, if found worse elsewhere, including a part of a completely distorted washer and a part of a zip tie inside of the magneto cover, it was making the bike discharge its cdi too soon and making a loud popping sound as an effect. The zip tie is still unknown to what and how it may of been involved.