Great stuff for what its good for, will take tar, tile adhesive, tree sap, and a host of other sticky garbage off a blade better than just about anything else. Great for drying out and waterproofing worn out spark plug cables long enough to get you home on a rainy day. Passable after-run spray for model airplane engines.
That said, I would not personally use it the way you did. Others may very well feel differently. My logic is this... if there is grit, especially metallic grit, in a knife what you need to do is first degrease the knife to so the grit does not stick, then get rid of all the grit. If you do this with water under pressure, or dry with compressed air, the knife is not lubricated at all, so you can easily tell if there is any grit left, or if it is completely clean. On the other hand, if you use WD40 as a pressure spray, you can never be sure you got out all the grit, because if any is left it will be lubricated enough so it will be unnoticable, but may still eventually cause damage. As I said, this is just my opinion. Hope it at least makes some sense to you.