Should I be worried?

I do not remember my additive being silver. The silver that you are seeing is probably aluminum, or bearing material, not steel.
As far as cutting a filter open, you need a filter cutter, not a hacksaw or something similar. How would determine which metal is what you are looking at?
You are probably okay, run it some more, and don't let it idle for 20 minutes, the cam lobes like to have oil thrown at them, unless it's a roller cam.