When drain oil, you will notice the plug is hard to come off by your fingers then you will know there is stripped threaded hole or drain plug. For mechanics.. is ignore them unless the drain plug (reuse) is not tighten by hand (use a ratchet or wrench), must fix the damaged threaded holes ( can use oversized plugs or replace oil pans). I've see the lube techs at Jiffy or quick lube shops, they use Grey RTV sealer to coating the head of drain plug and gasket on the pan, they doesn't want to see the customer's comeback for oil leaks.
The metallic come from moving parts such as bearings, timing chains, valve trains or cylinders/pistons common in first break-in run (new vehicles), most on the aluminum oil pans. Other problem is the most mechanics who didn't clean/wipe the drain plug/ pan before drain oil out of the pan or neglect the dirty like sand grits stick on the threaded drain plugs, and reuse damaged drain plugs.
If I see the RTV sealer coated on the head of the drain plug before servicing oil/filter change, must notify a customer first and advise to replace new plug or oil pan if the plug is stripped.