kaps:
A wise precaution, I would say. I believe lead stearate from primers is also a problem.
I have a bad habit when rimfire target shooting of easing back the bolt, then lifting the empty out with my right forefinger --- it saves scattering the brass with the ejector, which has to be picked up later. Then I'd often have a sandwich or something back in the clubhouse -- until I noticed the black ring on the pad of my forefinger. Now, that may be harmless, sooty residue, but I don't take the chance.
The drill is -- leave the firing line, rifle in the rack --- wash hands with soap -- eat sandwich.
B